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:
cbv beta iota delta [TODO projection TODO projection] in id, id'
DEBUG LTAC Evaluated term: a1
DEBUG LTAC Evaluated term: (list A)
Level 3: type of id
 has value 
(list A)