gen_bug.lean:9:2: error: tactic failed
A : Type,
B : Type,
a : A,
b : B,
H : @heq A a B b
⊢ @heq B b A a
gen_bug.lean:12:0: error: failed to add declaration 'tst' to environment, value has metavariables
  λ (A B : Type) (a : A) (b : B),
    ?M_1