Goal:
  
  A : Type
  f : A → A
  x : A
  l : list A
  p : f x = x
  X : All (λ x : A, f x = x) l
  IHX : map f l = l
  ============================
   (f x :: map f l = x :: l)


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