+++ /dev/null
-(**************************************************************************)
-(* ___ *)
-(* ||M|| *)
-(* ||A|| A project by Andrea Asperti *)
-(* ||T|| *)
-(* ||I|| Developers: *)
-(* ||T|| A.Asperti, C.Sacerdoti Coen, *)
-(* ||A|| E.Tassi, S.Zacchiroli *)
-(* \ / *)
-(* \ / This file is distributed under the terms of the *)
-(* v GNU Lesser General Public License Version 2.1 *)
-(* *)
-(**************************************************************************)
-
-set "baseuri" "cic:/matita/nat/exp".
-
-include "nat/div_and_mod.ma".
-
-let rec exp n m on m\def
- match m with
- [ O \Rightarrow (S O)
- | (S p) \Rightarrow (times n (exp n p)) ].
-
-interpretation "natural exponent" 'exp a b = (cic:/matita/nat/exp/exp.con a b).
-
-theorem exp_plus_times : \forall n,p,q:nat.
-n \sup (p + q) = (n \sup p) * (n \sup q).
-intros.elim p.
-simplify.rewrite < plus_n_O.reflexivity.
-simplify.rewrite > H.symmetry.
-apply assoc_times.
-qed.
-
-theorem exp_n_O : \forall n:nat. S O = n \sup O.
-intro.simplify.reflexivity.
-qed.
-
-theorem exp_n_SO : \forall n:nat. n = n \sup (S O).
-intro.simplify.rewrite < times_n_SO.reflexivity.
-qed.
-
-theorem exp_exp_times : \forall n,p,q:nat.
-(n \sup p) \sup q = n \sup (p * q).
-intros.
-elim q.simplify.rewrite < times_n_O.simplify.reflexivity.
-simplify.rewrite > H.rewrite < exp_plus_times.
-rewrite < times_n_Sm.reflexivity.
-qed.
-
-theorem lt_O_exp: \forall n,m:nat. O < n \to O < n \sup m.
-intros.elim m.simplify.unfold lt.apply le_n.
-simplify.unfold lt.rewrite > times_n_SO.
-apply le_times.assumption.assumption.
-qed.
-
-theorem lt_m_exp_nm: \forall n,m:nat. (S O) < n \to m < n \sup m.
-intros.elim m.simplify.unfold lt.reflexivity.
-simplify.unfold lt.
-apply (trans_le ? ((S(S O))*(S n1))).
-simplify.
-rewrite < plus_n_Sm.apply le_S_S.apply le_S_S.
-rewrite < sym_plus.
-apply le_plus_n.
-apply le_times.assumption.assumption.
-qed.
-
-theorem exp_to_eq_O: \forall n,m:nat. (S O) < n
-\to n \sup m = (S O) \to m = O.
-intros.apply antisym_le.apply le_S_S_to_le.
-rewrite < H1.change with (m < n \sup m).
-apply lt_m_exp_nm.assumption.
-apply le_O_n.
-qed.
-
-theorem injective_exp_r: \forall n:nat. (S O) < n \to
-injective nat nat (\lambda m:nat. n \sup m).
-simplify.intros 4.
-apply (nat_elim2 (\lambda x,y.n \sup x = n \sup y \to x = y)).
-intros.apply sym_eq.apply (exp_to_eq_O n).assumption.
-rewrite < H1.reflexivity.
-intros.apply (exp_to_eq_O n).assumption.assumption.
-intros.apply eq_f.
-apply H1.
-(* esprimere inj_times senza S *)
-cut (\forall a,b:nat.O < n \to n*a=n*b \to a=b).
-apply Hcut.simplify.unfold lt.apply le_S_S_to_le. apply le_S. assumption.
-assumption.
-intros 2.
-apply (nat_case n).
-intros.apply False_ind.apply (not_le_Sn_O O H3).
-intros.
-apply (inj_times_r m1).assumption.
-qed.
-
-variant inj_exp_r: \forall p:nat. (S O) < p \to \forall n,m:nat.
-p \sup n = p \sup m \to n = m \def
-injective_exp_r.