The Whiley Theorem Prover (WyTP) is an automatic and interactive theorem prover designed to discharge verification conditions generated by the Whiley Compiler. WyTP operates over a variant of first-order logic which includes integer arithmetic, arrays and quantification.
The following fails:
Presumably the reason is because the definition of
xs
is recursive. Certainly, if we swap it around soys
is being assigned then it passes: