gen_bug.lean:9:2: error:invalid 'generalize' tactic, type error
type mismatch at application
  @heq B b
term
  b
has type
  B_1
but is expected to have type
  B
proof state:
A B : Type,
a : A,
b : B,
H : @heq A a B b
⊢ @heq B b A a
gen_bug.lean:12:0: error: don't know how to synthesize placeholder
A B : Type,
a : A,
b : B
⊢ @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
remark: set 'formatter.hide_full_terms' to false to see the complete term
  ?M_1