CVC4Sy is a syntax-guided synthesis (SyGuS) solver based on bounded term enumeration and, for restricted fragments, quantifier elimination. The enumerative strategies are based on encoding term enumeration as an extension of the quantifier-free theory of algebraic datatypes and on a highly optimized brute-force algorithm. The quantifier elimination strategy extracts solutions from unsatisfiability proofs of the negated form of synthesis conjectures. It uses recent counterexample-guided techniques for quantifier instantiation that make finding such proofs practically feasible. CVC4Sy implements these strategies by extending the satisfiability modulo theories (SMT) solver CVC4. The strategy to be applied on a given problem is chosen heuristically based on the problem's structure. This document gives an overview of these techniques and their implementation in the SyGuS Solver CVC4Sy, an entry for SyGuS-Comp 2019.
