Remove traces of old KApp/MkApp constructors
Extend user-level equiv in nat.tt
Added 'when' patterns
Brazil literals are now expressions
Operations inside equiv_ty properly handled
Untested forall pattern for terms
Added - and * for nats; Added recursive fun
Added string constants to TT
Added pattern-matching in local lets
lambdas can be annotated by names
Nicer syntax for recursive local funs
nat.tt can satisfy its equiv