Goal:
  
  A : Type
  H : ReflectEq A
  a1 : A
  l1 : list A
  a2 : A
  l2 : list A
  Heq : (a1 == a2) = false
  l : list A
  Heqcall : ([], a1 :: l1, a2 :: l2) = split_prefix (a1 :: l1) (a2 :: l2)
  _x_ : list A
  _b_ : is_prefix _x_ l1
  eqa : a1 = a2
  _b1_ : is_prefix _x_ l2
  ============================
   (is_prefix (a1 :: _x_) (fst (fst (split_prefix (a1 :: l1) (a2 :: l2)))))


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2