https://github.com/tomprimozic/type-systems/tree/master/refined_types

>The implementation of a refined type-checker is actually very straightforward and turned out to be much simpler than I expected. Essentially, program expressions and contracts on function parameters and return types are converted into a series of mathematical formulas and logical statements, the validity of which is then assessed using an external automated theorem prover Z3.<

It seems possible to integrate Z3 with D contract programming.

Bye,
bearophile