Module CType <: DecTypeSig.
Definition t := type.
Definition eqb (t1 t2: type) :=
match t1, t2 with
| expr, expr => true
| context, context => true
| prog_state, prog_state => true
| _, _ => false
end.

Lemma eqb_spec: forall x y, Bool.reflect (x = y) (eqb x y).