include "nat/orders.ma".
include "datatypes/bool.ma".
+include "datatypes/compare.ma".
let rec leb n m \def
match n with
simplify.intros.apply H.apply le_S_S_to_le.assumption.
qed.
-theorem le_elim: \forall n,m:nat. \forall P:bool \to Prop.
+theorem leb_elim: \forall n,m:nat. \forall P:bool \to Prop.
((le n m) \to (P true)) \to ((Not (le n m)) \to (P false)) \to
P (leb n m).
intros.
apply (H1 H2).
qed.
+let rec nat_compare n m: compare \def
+match n with
+[ O \Rightarrow
+ match m with
+ [ O \Rightarrow EQ
+ | (S q) \Rightarrow LT ]
+| (S p) \Rightarrow
+ match m with
+ [ O \Rightarrow GT
+ | (S q) \Rightarrow nat_compare p q]].
+theorem nat_compare_n_n: \forall n:nat.(eq compare (nat_compare n n) EQ).
+intro.elim n.
+simplify.reflexivity.
+simplify.assumption.
+qed.
+
+theorem nat_compare_S_S: \forall n,m:nat.
+eq compare (nat_compare n m) (nat_compare (S n) (S m)).
+intros.simplify.reflexivity.
+qed.
+theorem nat_compare_to_Prop: \forall n,m:nat.
+match (nat_compare n m) with
+ [ LT \Rightarrow (lt n m)
+ | EQ \Rightarrow (eq nat n m)
+ | GT \Rightarrow (lt m n) ].
+intros.
+apply nat_elim2 (\lambda n,m.match (nat_compare n m) with
+ [ LT \Rightarrow (lt n m)
+ | EQ \Rightarrow (eq nat n m)
+ | GT \Rightarrow (lt m n) ]).
+intro.elim n1.simplify.reflexivity.
+simplify.apply le_S_S.apply le_O_n.
+intro.simplify.apply le_S_S. apply le_O_n.
+intros 2.simplify.elim (nat_compare n1 m1).
+simplify. apply le_S_S.apply H.
+simplify. apply le_S_S.apply H.
+simplify. apply eq_f. apply H.
+qed.
+
+theorem nat_compare_n_m_m_n: \forall n,m:nat.
+eq compare (nat_compare n m) (compare_invert (nat_compare m n)).
+intros.
+apply nat_elim2 (\lambda n,m.eq compare (nat_compare n m) (compare_invert (nat_compare m n))).
+intros.elim n1.simplify.reflexivity.
+simplify.reflexivity.
+intro.elim n1.simplify.reflexivity.
+simplify.reflexivity.
+intros.simplify.elim H.reflexivity.
+qed.
+
+theorem nat_compare_elim : \forall n,m:nat. \forall P:compare \to Prop.
+((lt n m) \to (P LT)) \to ((eq nat n m) \to (P EQ)) \to ((lt m n) \to (P GT)) \to
+(P (nat_compare n m)).
+intros.
+cut match (nat_compare n m) with
+[ LT \Rightarrow (lt n m)
+| EQ \Rightarrow (eq nat n m)
+| GT \Rightarrow (lt m n)] \to
+(P (nat_compare n m)).
+apply Hcut.apply nat_compare_to_Prop.
+elim (nat_compare n m).
+apply (H H3).
+apply (H2 H3).
+apply (H1 H3).
+qed.