this is already not recoverable and the z3 error is less helpfull

replace _ <- dbg ... with dbg_ ...
replace _ <- zipWithM ... with zipWithM_ ...

remove some debug output

This reverts commit de378efa.

this is no longer needed and is way faster without it

fix errors in the counterexample creation surrounding the "gen#" part added in some kinds of type variables

implement LetDestruct

Rename exprSort to inferType