Goal:
    X1' : list A.t  X1 : t  X : lt_ X1' X1
  ============================
   (forall x : t,
    {| pr1 := x; pr2 := x |} = {| pr1 := X1'; pr2 := X1 |} ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in False)


DEBUG:Going to execute:
hnf in id
Level 4: evaluation returns
hnf in id;
 match type of id with
 | sigma _ =>
     let xn := fresh id "'" in
     destruct id as [xn id]; DepElim.decompose_exists xn id;
      cbv beta iota delta [TODO projection TODO projection] in id, id';
      DepElim.decompose_exists id id'
 | _ => cbv beta iota delta [TODO projection TODO projection] in id, id'
 end
where
id' := X
of type
constr
id := X1
of type
constr of type tacvalue