Goal:
  
  A : Type
  H : ReflectEq A
  a1 : A
  l1 : list A
  a2 : A
  l2 : list A
  prefix : list A
  l1' : list A
  l2' : list A
  ============================
   (split_prefix l1 l2 = (prefix, l1', l2')
    → (∀ (H := CoreTactics.block) (l3 l4 l : list A),
         {| pr1 := l1; pr2 := l2 |} = {| pr1 := l3; pr2 := l4 |}
         → split_prefix l1 l2 = split_prefix l3 l4
           → let H0 := CoreTactics.block in
             is_prefix l l3
             → is_prefix l l4 → is_prefix l (fst (fst (split_prefix l3 l4))))
      → (a1 == a2) = true
        → ∀ (H := CoreTactics.block) (l3 l4 l : list A),
            {| pr1 := a1 :: l1; pr2 := a2 :: l2 |} =
            {| pr1 := l3; pr2 := l4 |}
            → (a1 :: prefix, l1', l2') = split_prefix l3 l4
              → let H0 := CoreTactics.block in
                is_prefix l l3
                → is_prefix l l4
                  → is_prefix l (fst (fst (split_prefix l3 l4))))


DEBUG:Going to execute:
simplify * || simplify ?; cbv beta