Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → C → Prop
  b : B
  l' : list B
  c : C
  l'' : list C
  f : Forall3 P [] (b :: l') (c :: l'')
  ============================
   (All3 P [] (b :: l') (c :: l''))


DEBUG:Going to execute:
constructor
Level 0: Backtrace:

In environment
A : Type
B : Type
C : Type
P : A → B → C → Prop
b : B
l' : list B
f : Forall3 P [] (b :: l') []
Unable to unify
 "All3 ?M2765 (?M2766 :: ?M2769) (?M2767 :: ?M2770) (?M2768 :: ?M2771)"
with "All3 P [] (b :: l') []".
Level 0: Backtrace:

In environment
A : Type
B : Type
C : Type
P : A → B → C → Prop
b : B
l' : list B
f : Forall3 P [] (b :: l') []
Unable to unify
 "All3 ?M2765 (?M2766 :: ?M2769) (?M2767 :: ?M2770) (?M2768 :: ?M2771)"
with "All3 P [] (b :: l') []".