Goal:
    A : Type  P : A → Type  a : A  x : A  l : list A  p : P x  X : All P l
  ============================
   ([a] = x :: l
    → let H := CoreTactics.block in let H0 := CoreTactics.block in P a)


DEBUG:Going to execute:
DepElim.simplify_one_dep_elim