t_rect = 
fun (P : t -> Type) (f : let x := t in forall x0 : x, P x0 -> P (k x0)) =>
fix F (t : t) : P t :=
  match t as t0 return (P t0) with
  | k _ x0 => f x0 (F x0)
  end
     : forall P : t -> Type,
       (let x := t in forall x0 : x, P x0 -> P (k x0)) -> forall t : t, P t
proj = 
fun (x y : nat) (P : nat -> Type) (def : P x) (prf : P y) =>
match eq_nat_dec x y with
| left eqprf => match eqprf in (_ = z) return (P z) with
                | eq_refl => def
                end
| right _ => prf
end
     : forall (x y : nat) (P : nat -> Type), P x -> P y -> P y

Argument scopes are [nat_scope nat_scope _ _ _]
foo = 
fix foo (A : Type) (l : list A) {struct l} : option A :=
  match l with
  | nil => None
  | x0 :: nil => Some x0
  | x0 :: (_ :: _) as l0 => foo A l0
  end
     : forall A : Type, list A -> option A

Argument scopes are [type_scope list_scope]
foo' = if A 0 then true else false
     : bool