The subject of this dissertation is fiscal policy in the United States. In recent years the limitations of monetary policy have become more evident, generating greater interest in the use of fiscal policy as a stabilization tool. Despite considerable advances in the fiscal policy literature, many important questions about the effects and implementation of such policy remain unresolved. This motivates the present work, which explores both topics in the chapters that follow. I begin in the second chapter by estimating Federal Reserve responses to changes in taxes and spending. Monetary responses are a critical determinant of fiscal policy effectiveness since central banks have the ability to offset many of the economic changes resulting from fiscal shocks. Using techniques commonly employed in the fiscal multiplier literature, my results indicate a willingness by monetary policymakers to alter policy directly in response to fiscal shocks in a way that either reinforces or counteracts the resulting effects. In the third and fourth chapters I shift my focus to the conduct of fiscal policy. Specifically, I use Bayesian methods to estimate the response of federal discretionary policy to different macroeconomic variables. I allow for uncertainty about various characteristics of the underlying model which enables me to determine, for example, which variables matter to policymakers; whether policy conduct has changed over time; and whether policy responses are state dependent. My results indicate, among other things, that policy responds countercyclically to changes in the labor market, but only during periods of weak economic activity.

The study sought to test the applicability of the Hotelling rule in South Africa. In environmental economics, the Hotelling rule has come to be a pillar of the exhaustible resources framework and in addition to this, it has presented essential insights into the consumption and extraction of non-renewable resources. Hotelling sought to address one important question which had been unanswered regarding the depletion of exhaustible resources: How much of the natural resource in question should be consumed presently and how much of it should be stocked up for future generations? The focus was to find a solution for those involved in the exploitation of natural resources to choose between the current value of the natural resource if extracted and sold and the future increased value of the asset if left unexploited. According to the Hotelling rule, the extraction path in competitive market economies will, under certain circumstances, be socially optimal. An extraction path that is not socially optimal compromises the welfare of future generations. The welfare of South Africa’s present population and more especially in the future will be greatly determined by the stock of natural resources available and the quality of the environment. Currently, the production processes deplete natural resources. Concern with the supposed increasing scarcity of gold in South Africa, and the possibility of running out of gold, has become a source of concern. South Africa’s gold reserves (gold in the ground that can be extracted profitably) are becoming depleted at an alarming rate. Most reserves are already exhausted; and the costs involved in mining lower-grade ore, and deposits located very deep in the ground, are becoming excessive. In light of this, this study sought to test the applicability of the Hotelling rule in South Africa. In order to empirically test the Hotelling rule, the study was guided by previous literature that had sought to test it. In this regard, the study used both descriptive and inferential statistics. The study has three data analysis chapters. The first two presented and examined the time series properties of gold prices, gold production and gold consumption. The third data analysis chapter examined the relationship between gold price and interest rates. In the first two data analysis chapters, visual inspection, growth rates, variance ratio tests and advanced unit root tests were used to examine the time series properties of gold prices, gold production and gold consumption. Results showed that the behaviour of the gold price series and gold production series in South Africa have a behaviour that is socially optimal. This is in line with the Hotelling rule. The rule predicts exponentially increasing resource prices and this result in mineral resources following the path of the positive trend. The positive trend is prompted by the increasing price reflecting the increasing scarcity of the resource. However, consumption trends were seen to be violating the Hotelling rule. The Hotelling rule predicts that the price increases until it eventually reaches the choke price, where the quantity demanded decreases to zero. However, in contrast to this, results showed that the demand for gold has been increasing instead of decreasing. This is not in line with the Hotelling rule. Furthermore the relationship between interest rate and gold price was negative and this suggested that the price of gold was not rising at the rate of the interest rate. The results of the study suggested that gold production is not following a social optimally path. The study recommended that the government come up with measures that prolong the lifespan of the gold reserves. These included research and development to promote technological innovations in the mining sector. This may make it possible for firms to access lower-grade ores. The study also recommended that since the Hotelling rule partly applied in the gold sector, there is a need to adopt some other theoretical measures that can ensure that the proceeds from the gold taxes are used in the most effective way.

O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

In academia, after a reasonable probationary period of service and upon the achievement of tenure, the recipients of tenure are entitled to a continuing appointment at an institution without mandatory retirement and with only limited grounds for revocation. Advocates of tenure argued that it protected academic freedom through economic security. Opponents of tenure argued that it fostered inefficient and unproductive behavior. This dissertation developed a framework for examining academic tenure in U.S. economics departments. I constructed a dataset of tenured U.S. economics professors who were Ph.D. recipients between 1990 and 2006 and tracked their publications. In the first chapter, based on difference-in-difference analysis I found that tenure has a direct effect on the choice of research direction/focus. In general, tenured groups had a higher degree of specialization than non-tenured groups after they received tenure. For some tenured groups, even if their extent of specialization decreased after tenure, when I controlled for unobserved heterogeneity, tenure still had a positive effect on extent of specialization. This result suggested that the job security provided by tenure made tenured faculty more narrowly focused on their research. Using path analysis in the second chapter, my finding suggested that the extent of specialization was one of the key factors which might influence a scholar’s productivity. In addition, the extent of specialization helped explain gender differences in academic productivity. The results revealed that the effect of gender on productivity through the degree of specialization was more notable among older generations, and in most fields, gender differences in extent of research specialization mediated gender difference in research performance; although there were some fields in which gender difference in the research process could not explain gender difference in research performance. The third chapter expanded our understanding of advancement in academics by exploring a new dimension of inquiry: whether the extent of specialization in scholars’ research programs improved promotion prospects. Using discrete event analysis, my research showed that the extent of research specialization contributed to career acceleration, although gender difference on the prospects of advancement in academics was not significant.

The objective of this study is to understand the dynamics of international monetary policy and the relationship that exists between larger more developed economies and smaller less developed economies within a policy context. The 2008 financial crisis has caused intense revival of Austrian economics due to the monetary nature of the recession caused as a subsequent effect of the stock/housing market collapse that occurred in 2007. One factor of the 2008 financial crisis that created intense concern was the extent to which the slowdown in economic activity was able to be transmitted across international borders. The South African economy was not isolated from the financial crisis by any means and experienced a significant slowdown in economic growth. By making use of data collected from the Federal Reserve Bank of St. Louis and the appropriate econometric techniques, a model is developed to study the dynamics between United States monetary policy and the South African economy. The Austrian School provides a sound theoretical framework that allows for the specification of testable propositions to verify the validity of an “Austrian” internationally transmitted business cycle. Using United States money supply, South African private consumption, South African gross fixed capital formation and the South African current account, a vector autoregressive model is specified to analyse the dynamics behind the United States and South African economy. The results of the empirical test all confirm the theoretical prescriptions developed in the literature review that monetary growth in the United States raise consumption, investment and improve the current account balance in the South African economy. This is a novel result for this study as it confirms that a large central economy has the ability to trigger economic expansions in a peripheral economy. This study further points out the inefficiencies associated with Keynesian style policy making and propagates for a movement towards a more prudent Austrian approach. Keynesian policy making through demand oriented policies have historically been more concerned with “curing” economic instability rather than preventing it. In light of this, the need for economic reform specifically within the manner in which monetary policy is conducted is evident. Aggressive monetary policy in the wake of economic slowdown is no longer effective at creating a sustainable and stable economic environment. A movement away from the monopolization of money and central economic decision making is necessary if the global economy wishes to reach economic permanence.

In this thesis we have presented econometrics and forecasts of Bitcoin and Google (GOOG) prices. We have implemented two models, one traditional, “ARIMA” and a relatively new one, “Prophet model” by using Facebook Prophet (ML). Machine learning is still new in the economic field, it has been rewarding to learn its capability. We have evaluated the model’s performance by using root mean square error (RMSE) and compared the result which model performed better. We wanted to compare to different assets, volatile Bitcoin to considerable stable Google (GOOG), thus investigate our models performance and if they differ or not. Regarding our result, we found that the ARIMA models have the best forecasting ability. We also investigate the impact of rational expectation and its impact on an asset price. We found that announcements on Bitcoin cause a significantly change in price and had an impact on the model’s performance. / I denna avhandling har vi presenterat ekonometriska modeller och prognoserade prisnivåer av Bitcoins och Googles (GOOG). Vi har implementerat två modeller, en traditionell, "ARIMA" samt en relativt ny modell, "Profetmodellen" med Facebook Prophet (ML). Maskininlärning är fortfarande nytt inom det ekonomiska området och det har varit givande att förstå dess förmåga. Vi vill jämföra två typer av tillgångar, Bitcoin som är volatile mot Google som är förhållandevis stabil för att se om våra modeller skiljer sig åt. Vi har utvärderat modellens prestanda med hjälp av root mean square error (RMSE) och jämförde resultatet vilken modell som var mest exakt. Vi fann att ARIMA-modellen gav oss bäst resultat. Vi undersöker också effekterna av rationella förväntningar och dess inverkan på pris av tillgång. Vi fann att nyheter om Bitcoin influerar dess pris och hade en inverkan på modellernas prestanda.

My dissertation explores two broad areas in econometrics and statistics. The first area is nonparametric identification and estimation with endogeneity using instrumental variables. The second area is related to low-rank matrix recovery and high-dimensional panel data models. The following three chapters study different topics in these areas. Chapter 1 considers identification and estimation of triangular models with a discrete endogenous variable and an instrumental variable (IV) taking on fewer values. Using standard approaches, the small support set of the IV leads to under-identification due to the failure of the order condition. This chapter develops the first approach to restore identification for both separable and nonseparable models in this case by supplementing the IV with covariates, allowed to enter the model in an arbitrary way. For the separable model, I show that it satisfies a system of linear equations, yielding a simple identification condition and a closed-form estimator. For the nonseparable model, I develop a new identification argument by exploiting its continuity and monotonicity, leading to weak sufficient conditions for global identification. Built on it, I propose a uniformly consistent and asymptotically normal sieve estimator. I apply my approach to an empirical application of the return to education with a binary IV. Though under-identified by the IV alone, I obtain results consistent with the empirical literature using my method. I also illustrate the applicability of the approach via an application of preschool program selection where the supplementation procedure fails. Chapter 2, written with Jushan Bai, studies low-rank matrix recovery with a non-sparse error matrix. Sparsity or approximate sparsity is often imposed on the error matrix for low-rank matrix recovery in statistics and machine learning literature. In econometrics, on the other hand, it is more common to impose a location normalization for the stochastic errors. This chapter sheds light on the deep connection between the median zero assumption and the sparsity-type assumptions by showing that the principal component pursuit method, a popular approach for low-rank matrix recovery by Candès et al. (2011), consistently estimates the low-rank component under a median zero assumption. The proof relies on a new theoretical argument showing that the median-zero error matrix can be decomposed into a matrix with a sufficient number of zeros and a non-sparse matrix with a small norm that controls the estimation error bound. As no restriction is imposed on the moments of the errors, the results apply to cases when the errors have heavy- or fat-tails. In Chapter 3, I consider nuclear norm penalized quantile regression for large N and large T panel data models with interactive fixed effects. As the interactive fixed effects form a low-rank matrix, inspired by the median-zero interpretation, the estimator in this chapter extends the one studied in Chapter 2 by incorporating a conditional quantile restriction given covariates. The estimator solves a global convex minimization problem, not requiring pre-estimation of the (number of the) fixed effects. Uniform rates are obtained for both the slope coefficients and the low-rank common component of the interactive fixed effects. The rate of the latter is nearly optimal. To derive the rates, I show new results that establish uniform bounds of norms of certain random matrices of jump processes. The performance of the estimator is illustrated by Monte Carlo simulations.

Recent decades have seen great advances in the methods we use to understand cause and effect in the world of work. Building on that tradition, this dissertation explores two broad topics in econometrics as tools to address specific questions in labor economics. The main econometric contributions are to extend identification results for research designs based on bunching (Chapter 1) and those that make use of instrumental variables (Chapters 2 and 3). The empirical questions that compel them are described below. Chapter 1 examines the effect of overtime regulation on hours of work in the United States, extending a recently popularized technique that uses bunching observed at kinks in agents' choice sets for identification. In the U.S., most workers are required to be paid one-and-a-half times their typical rate of pay for any hours in excess of forty within a week. While prominent and long-standing, this policy has not been meaningfully reformed since it was first established at the federal level in 1938. As a result, few studies have been able to leverage causal research designs to assess its labor market impacts. I use bunching in the distribution of weekly hours at forty--where the policy introduces a convex "kink" in firms' costs--to estimate this effect. To do so, I develop a framework in which bunching at a choice-set kink is informative about causal effects under substantially weaker assumptions than those maintained in existing work. This allows the effect of the overtime policy to be partially identified without making parametric assumptions about firms' objective functions, or about the distribution of hours they would set in the absence of the policy. Using an administrative dataset of weekly hours derived from payroll records, I find that the bounds are informative and that covered hourly workers in the U.S. work an average of at least half an hour less as a result, in affected weeks. Chapter 2 turns to a still-more popular strategy in applied microeconomics: the instrumental variables research design. I propose a new method for estimating causal effects when a researcher has more than one such instrument, and apply it to reassess the labor market returns to college education. The method is motivated by the following issue. When treatment effects are heterogeneous, it is known that instruments can be used to identify local average treatment effects under an assumption known as "monotonicity”. However, when a researcher wishes to use multiple instruments together, this assumption can become quite restrictive, and empirical conclusions may be misleading if it is violated. I propose an alternative assumption that I call "vector monotonicity", which is quite natural in typical settings with multiple instruments. I show that vector monotonicity leads to identification of a useful class of treatment effect parameters, but the two-stage-least-squares estimator popular in applied work does not consistently estimate them. I propose an alternative estimator, and apply it to the classic question of the returns to schooling. I find that the approach based upon vector monotonicity reveals new patterns of heterogeneity in the earnings effect of college education. Chapter 3, with coauthors Ashna Arora and Jonas Hjort, considers the effects of a worker's first job on outcomes later in their career. This is typically a difficult question to answer empirically, as workers entering the labor force are not randomly assigned to employers. We make use of a unique opportunity to study this question in the context of medical residencies in Norway. For decades, medical school graduates in Norway were matched to residencies based on a random serial dictatorship mechanism, in which doctors could choose--in an order determined by lottery--among available positions in the country. We develop an econometric framework in which the random choice set a doctor is presented with provides a collection of instruments for their choice of residency hospital, and hence first job as a doctor. Because we only observe choices and not a doctor’s full preferences, this requires new methods--related to those of Chapter 2. We find persistent effects of a doctor’s first job on earnings, specializations, and mid-career moves. We use the estimates to assess the replacement of the serial-dictatorship by a decentralized labor market in 2013, which we find led to a small increase in resident welfare.