(* SUCCESSOR FOR NON-NEGATIVE INTEGERS **************************************)
-definition nsucc: nat → nat ≝ λm. match m with
-[ nzero ⇒ ninj (𝟏)
-| ninj p ⇒ ninj (↑p)
+definition npsucc (m): pnat ≝
+match m with
+[ nzero ⇒ 𝟏
+| ninj p ⇒ ↑p
].
+interpretation
+ "positive successor (non-negative integers)"
+ 'UpArrow m = (npsucc m).
+
+definition nsucc (m): nat ≝
+ ninj (↑m).
+
interpretation
"successor (non-negative integers)"
'UpArrow m = (nsucc m).
-(* Basic rewrites ***********************************************************)
+(* Basic constructions ******************************************************)
+
+lemma npsucc_zero: (𝟏) = ↑𝟎.
+// qed.
+
+lemma npsucc_inj (p): (↑p) = ↑(ninj p).
+// qed.
lemma nsucc_zero: ninj (𝟏) = ↑𝟎.
// qed.
lemma nsucc_inj (p): ninj (↑p) = ↑(ninj p).
// qed.
+lemma npsucc_succ (n): psucc (npsucc n) = npsucc (nsucc n).
+// qed.
+
(* Basic eliminations *******************************************************)
(*** nat_ind *)
-lemma nat_ind (Q:predicate …):
+lemma nat_ind_succ (Q:predicate …):
Q (𝟎) → (∀n. Q n → Q (↑n)) → ∀n. Q n.
#Q #IH1 #IH2 * //
#p elim p -p /2 width=1 by/
qed-.
(*** nat_elim2 *)
-lemma nat_ind_2 (Q:relation2 …):
+lemma nat_ind_2_succ (Q:relation2 …):
(∀n. Q (𝟎) n) →
- (∀m. Q (↑m) (𝟎)) →
+ (∀m. Q m (𝟎) → Q (↑m) (𝟎)) →
(∀m,n. Q m n → Q (↑m) (↑n)) →
∀m,n. Q m n.
-#Q #IH1 #IH2 #IH3 #m elim m -m [ // ]
-#m #IH #n elim n -n /2 width=1 by/
+#Q #IH1 #IH2 #IH3 #m @(nat_ind_succ … m) -m [ // ]
+#m #IH #n @(nat_ind_succ … n) -n /2 width=1 by/
qed-.
-(* Basic inversions ***************************************************************)
+(* Basic inversions *********************************************************)
-(*** injective_S *)
-lemma eq_inv_nsucc_bi: injective … nsucc.
+lemma eq_inv_npsucc_bi: injective … npsucc.
* [| #p1 ] * [2,4: #p2 ]
-[1,4: <nsucc_zero <nsucc_inj #H destruct
-| <nsucc_inj <nsucc_inj #H destruct //
+[ 1,4: <npsucc_zero <npsucc_inj #H destruct
+| <npsucc_inj <npsucc_inj #H destruct //
| //
]
qed-.
+(*** injective_S *)
+lemma eq_inv_nsucc_bi: injective … nsucc.
+#n1 #n2 #H
+@eq_inv_npsucc_bi @eq_inv_ninj_bi @H
+qed-.
+
lemma eq_inv_nsucc_zero (m): ↑m = 𝟎 → ⊥.
* [ <nsucc_zero | #p <nsucc_inj ] #H destruct
qed-.
-lemma eq_inv_nzero_succ (m): 𝟎 = ↑m → ⊥.
+lemma eq_inv_zero_nsucc (m): 𝟎 = ↑m → ⊥.
* [ <nsucc_zero | #p <nsucc_inj ] #H destruct
qed-.
+
+(*** succ_inv_refl_sn *)
+lemma nsucc_inv_refl (n): n = ↑n → ⊥.
+#n @(nat_ind_succ … n) -n
+[ /2 width=2 by eq_inv_zero_nsucc/
+| #n #IH #H /3 width=1 by eq_inv_nsucc_bi/
+]
+qed-.