Goal:
    A : Type  P : list A → A → Type  x : A  a1 : list A  a : All_fold P a1
  ============================
   ([x] = a1
    → let H := CoreTactics.block in let H0 := CoreTactics.block in P [] x)


DEBUG:Going to execute:
let eliminator := eval simpl in DepElim.elim in
           tac p eliminator
DEBUG LTAC Evaluated term: a
DEBUG LTAC Evaluated term: (All_fold P a1)