1 (**************************************************************************)
4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| The HELM team. *)
8 (* ||A|| http://helm.cs.unibo.it *)
10 (* \ / This file is distributed under the terms of the *)
11 (* v GNU General Public License Version 2 *)
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15 include "lambda/rc_sat.ma".
17 (* THE EVALUATION *************************************************************)
19 (* The interpretation of a type t as a r.c. denoted by 〚t〛.
20 * For the "conv" rule we need 〚M〛 ≈ 〚N〛 when M and N are convertible, so:
21 * 1) 〚(λB.M N)〛 ≈ 〚N[0≝N]〛 implies that 〚(M N)〛 and 〚λB.M〛 are evaluated by
22 * stacking the application arguments like a reduction machine does
23 * 2) ∀M,N. 〚D M〛 ≈ 〚D N〛, implies that 〚D M〛 must be a constant.
25 let rec ev E K t on t : RC ≝ match t with (* E: environment, K: stack *)
26 [ Sort _ ⇒ snRC (* from λ→ *)
27 | Rel i ⇒ nth i … E snRC (* from F *)
28 | App M N ⇒ ev E (ev E ([]) N :: K) M (* machine-like push *)
29 | Lambda _ M ⇒ ev (hd … K snRC :: E) (tail … K) M (* machine-like pop *)
30 | Prod N M ⇒ let C ≝ (ev E ([]) N) in
31 depRC C (ev (C :: E) K M) (* from λ→ and F *)
32 | D _ ⇒ snRC (* see note 2 above *)
35 interpretation "interpretation of a type" 'Eval2 t E K = (ev E K t).
37 (* extensional equality of the interpretations *)
38 definition eveq: T → T → Prop ≝ λt1,t2. ∀E,K. 〚t1〛_[E, K] ≅ 〚t2〛_[E, K].
41 "extensional equality of the type interpretations"
42 'napart t1 t2 = (eveq t1 t2).
44 (* The interpretation of a context of types as a context of r.c.'s *)
45 let rec cev E G on G : list RC ≝ match G with
47 | cons t F ⇒ let D ≝ cev E F in 〚t〛_[D,[]] :: D
50 interpretation "interpretation of a context" 'Eval1 G E = (cev E G).
52 theorem ev_app: ∀M,N,E,K. 〚App M N〛_[E, K] = 〚M〛_[E, 〚N〛_[E,[]]::K].
55 theorem ev_lambda: ∀M,N,E,K.
56 〚Lambda N M〛_[E, K] = 〚M〛_[hd … K snRC :: E, tail … K].
59 theorem ev_prod: ∀M,N,E,K.
60 〚Prod N M〛_[E,K] = depRC (〚N〛_[E,[]]) (〚M〛_[〚N〛_[E,[]]::E,K]).
63 theorem ev_repl: ∀t,E1,E2,K1,K2. E1 ≅ E2 → K1 ≅ K2 → 〚t〛_[E1,K1] ≅ 〚t〛_[E2,K2].
67 theorem ev_rel_lt: ∀K,D,E,i. (S i) ≤ |E| → 〚Rel i〛_[E @ D, K] = 〚Rel i〛_[E,K].
68 #K #D #E (elim E) -E [1: #i #Hie (elim (not_le_Sn_O i)) #Hi (elim (Hi Hie)) ]
69 #C #F #IHE #i (elim i) -i // #i #_ #Hie @IHE @le_S_S_to_le @Hie
72 theorem ev_rel_ge: ∀K,D,E,i. (S i) ≰ |E| →
73 〚Rel i〛_[E @ D, K] = 〚Rel (i-|E|)〛_[D,K].
74 #K #D #E (elim E) -E [ normalize // ]
75 #C #F #IHE #i (elim i) -i [1: -IHE #Hie (elim Hie) -Hie #Hie (elim (Hie ?)) /2/ ]
76 normalize #i #_ #Hie @IHE /2/
79 theorem ev_app_repl: ∀M1,M2,N1,N2. M1 ≈ M2 → N1 ≈ N2 →
80 App M1 N1 ≈ App M2 N2.
81 #M1 #M2 #N1 #N2 #IHM #IHN #E #K >ev_app (@transitive_rceq) /3/
84 theorem ev_lambda_repl: ∀N1,N2,M1,M2. N1 ≈ N2 → M1 ≈ M2 →
85 Lambda N1 M1 ≈ Lambda N2 M2.
86 #N1 #N2 #M1 #M2 #IHN #IHM #E #K >ev_lambda (@transitive_rceq) //
89 theorem ev_prod_repl: ∀N1,N2,M1,M2. N1 ≈ N2 → M1 ≈ M2 →
90 Prod N1 M1 ≈ Prod N2 M2.
91 #N1 #N2 #M1 #M2 #IHN #IHM #E #K >ev_prod @dep_repl //
92 (@transitive_rceq) [2: @IHM | skip ] /3/
95 (* weakeing and thinning lemma for the type interpretation *)
96 (* NOTE: >commutative_plus comes from |a::b| ↦ S |b| rather than |b| + 1 *)
97 theorem ev_lift: ∀E,Ep,t,Ek,K.
98 〚lift t (|Ek|) (|Ep|)〛_[Ek @ Ep @ E, K] ≅ 〚t〛_[Ek @ E, K].
100 [ #n >lift_sort /by SAT0_sort/
101 | #i #Ek #K @(leb_elim (S i) (|Ek|)) #Hik
102 [ >(lift_rel_lt … Hik) >(ev_rel_lt … Hik) >(ev_rel_lt … Hik) //
103 | >(lift_rel_ge … Hik) >(ev_rel_ge … Hik) <associative_append
104 >(ev_rel_ge …) (>length_append)
105 [ >arith2 // @not_lt_to_le /2/ | @(arith3 … Hik) ]
107 | #M #N #IHM #IHN #Ek #K >lift_app >ev_app (@transitive_rceq) /3/
108 | #N #M #IHN #IHM #Ek #K >lift_lambda >ev_lambda (@transitive_rceq)
109 [2: >commutative_plus @(IHM (? :: ?)) | skip ] //
110 | #N #M #IHN #IHM #Ek #K >lift_prod >ev_prod (@dep_repl) //
111 (@transitive_rceq) [2: >commutative_plus @(IHM (? :: ?)) | skip ] /3/
117 theorem tj_ev: ∀G,A,B. G ⊢A:B → ∀H,l. l ∈ 〚G〛_(H) → A[l] ∈ 〚B[l]〛_〚G〛_(H).
118 #G #A #B #tjAB (elim tjAB) -G A B tjAB
119 [ #i #j #_ #H #l #_ >substc_sort >substc_sort /2 by SAT0_sort/
120 | #G #B #n #tjB #IH #H #l (elim l) -l (normalize)
122 | #C #D #IHl #mem (elim mem) -mem #mem #memc
123 >lift_0 >delift // >lift_0
127 theorem tj_sn: ∀G,A,B. G ⊢A:B → SN A.
128 #G #A #B #tjAB lapply (tj_trc … tjAB (nil ?) (nil ?)) -tjAB (normalize) /3/
133 theorem tev_rel_S: ∀i,R,H. 〚Rel (S i)〛_(R::H) = 〚Rel i〛_(H).
137 theorem append_cons: ∀(A:Type[0]). ∀(l1,l2:list A). ∀a.
138 (a :: l1) @ l2 = a :: (l1 @ l2).