Expander2 as a Prover and Rewriter

Expander2 is a flexible multi-purpose workbench for interactive rewriting, verification, constraint solving, flow graph analysis and other procedures that build up proofs or computation sequences. Moreover, tailormade interpreters display terms as two-dimensional structures ranging from trees and rooted graphs to a variety of pictorial representations that include tables, matrices, alignments, partitions, fractals and turtle systems. Proofs and computations performed with Expander2 follow the rules and the semantics of swinging types. Swinging types are based on manysorted predicate logic and combine constructor-based types with destructorbased (e.g. state-based) ones. The former come as initial term models, the latter as final models consisting of context interpretations. Relation symbols are interpreted as least or greatest solutions of their respective axioms. This paper presents an overview of Expander2 with particular emphasis on the system’s prover and rewriter capabilities.