We describe contributions to algorithmic proof techniques for deciding the satisfiability of boolean combinations of many-variable nonlinear polynomial equations and inequalities over the real and complex numbers. In the first half, we present an abstract theory of Grobner basis construction algorithms for algebraically closed fields of characteristic zero and use it to introduce and prove the correctness of Grobner basis methods tailored to the needs of modern satisfiability modulo theories (SMT) solvers. In the process, we use the technique of proof orders to derive a generalisation of S-polynomial superfluousness in terms of transfinite induction along an ordinal parameterised by a monomial order. We use this generalisation to prove the abstract (“strategy-independent”) admissibility of a number of superfluous S-polynomial criteria important for efficient basis construction. Finally, we consider local notions of proof minimality for weak Nullstellensatz proofs and give ideal-theoretic methods for computing complex “unsatisfiable cores” which contribute to efficient SMT solving in the context of nonlinear complex arithmetic. In the second half, we consider the problem of effectively combining a heterogeneous collection of decision techniques for fragments of the existential theory of real closed fields. We propose and investigate a number of novel combined decision methods and implement them in our proof tool RAHD (Real Algebra in High Dimensions). We build a hierarchy of increasingly powerful combined decision methods, culminating in a generalisation of partial cylindrical algebraic decomposition (CAD) which we call Abstract Partial CAD. This generalisation incorporates the use of arbitrary sound but possibly incomplete proof procedures for the existential theory of real closed fields as first-class functional parameters for “short-circuiting” expensive computations during the lifting phase of CAD. Identifying these proof procedure parameters formally with RAHD proof strategies, we implement the method in RAHD for the case of full-dimensional cell decompositions and investigate its efficacy with respect to the Brown-McCallum projection operator. We end with some wishes for the future.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Esta dissertaÃÃo està baseada em uma sÃrie de trabalhos publicados por H. Delfs e M. Knebusch sobre uma teoria de homologia para espaÃos semialgÃbricos sobre corpos reais fechados. Neste trabalho, reunimos as definiÃÃes e principais resultados sobre a teoria de homologia semialgÃbrica. AlÃm dissso, como aplicaÃÃo dessa teoria, trazemos uma prova do Teorema de Ax-Grothendick para aplicaÃÃes polinomiais sobre corpos reais fechados. / This thesis is based on a series of papers published by H. Delfs and M. Knebusch on a homology theory to semialgebraic spaces on real closed fields. In this work, we collect the definitions and main results on the theory of semialgebraic homology. Furthermore, as application of this theory, we present a proof of the theorem of Ax-Grothendick for polynomials applications on real closed fields.