Goal:
  
  x : t
  X1 : sigma (fun _ : t => t)
  X2 : (fun index : sigma (fun _ : t => t) => lt_ (pr1 index) (pr2 index)) X1
  ============================
   ({| pr1 := x; pr2 := x |} = X1 ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in False)


DEBUG:Going to execute:
try unfold signature in id'2