Goal:
    A : Type  B : Type  C : Type  p : A → B → C → bool  H : is_true true
  ============================
   (All3 (λ (x : A) (y : B) (z : C), p x y z) [] [] [])


DEBUG:Going to execute:
<coq-core.plugins.ltac::constructor@0>
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

Tactic failure: congruence failed.