Section Transport.
(* semi-unification solution *)
Variables φ ψ0 ψ1 : nat -> SU.term.
Variable Hφψ0 : SU.substitute ψ0 (SU.substitute φ SUs) = SU.substitute φ SUt0.
Variable Hφψ1 : SU.substitute ψ1 (SU.substitute φ SUs) = SU.substitute φ SUt1.
Definition t_x_W' := SU_term_to_poly_type (SU.substitute φ SUs).
Definition n_W' := locked (poly_var_bound (poly_arr t_x_W' t_x_W')).
Definition t_x_W : poly_type := many_poly_abs n_W' (poly_arr t_x_W' t_x_W').
Definition t_x_0_W : poly_type := SU_term_to_poly_type (SU.substitute φ SUt0).
Definition t_x_1_W : poly_type := SU_term_to_poly_type (SU.substitute φ SUt1).
Definition ts_0_W : list poly_type := map (fun n => SU_term_to_poly_type (φ n)) (rev (seq 0 n_W)).
Definition ts_1_W : list poly_type := map (fun n => SU_term_to_poly_type (ψ0 n)) (rev (seq 0 n_W')).
Definition ts_2_W : list poly_type := map (fun n => SU_term_to_poly_type (ψ1 n)) (rev (seq 0 n_W')).
Definition x_1_W : term := many_ty_app (var 0) ts_1_W.
Definition x_2_W : term := many_ty_app (var 0) ts_2_W.
Definition Q_W : term := abs t_x_W (many_ty_abs n_W' (app (app (many_ty_app (var 2) ts_0_W) x_1_W) x_2_W)).
(* correctly annotated M_W, similar to Wells' construction *)
Definition P_W : term := app (ty_app (ty_app (var 0) (poly_var 0)) t_x_W) Q_W.
Fact poly_var_bound_SUt0'_n_W : poly_var_bound SUt0' < n_W.
Fact poly_arr_eq_eq {s t} : s = t -> poly_arr s s = poly_arr t t.

Lemma pure_typable_M_W :
typing Gamma_W P_W (poly_var 0) ->
pure_typable Gamma_W M_W.