--- /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 *)
+(* *)
+(**************************************************************************)
+
+include "nat/div_and_mod.ma".
+include "nat/lt_arith.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_SO_n : \forall n:nat. S O = (S O) \sup n.
+intro.elim n
+ [reflexivity
+ |simplify.rewrite < plus_n_O.assumption
+ ]
+qed.
+
+theorem exp_SSO: \forall n. exp n (S(S O)) = n*n.
+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.apply le_n.
+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.
+
+theorem le_exp: \forall n,m,p:nat. O < p \to n \le m \to exp p n \le exp p m.
+apply nat_elim2
+ [intros.
+ apply lt_O_exp.assumption
+ |intros.
+ apply False_ind.
+ apply (le_to_not_lt ? ? ? H1).
+ apply le_O_n
+ |intros.
+ simplify.
+ apply le_times
+ [apply le_n
+ |apply H[assumption|apply le_S_S_to_le.assumption]
+ ]
+ ]
+qed.
+
+theorem lt_exp: \forall n,m,p:nat. S O < p \to n < m \to exp p n < exp p m.
+apply nat_elim2
+ [intros.
+ apply (lt_O_n_elim ? H1).intro.
+ simplify.unfold lt.
+ rewrite > times_n_SO.
+ apply le_times
+ [assumption
+ |apply lt_O_exp.
+ apply (trans_lt ? (S O))[apply le_n|assumption]
+ ]
+ |intros.
+ apply False_ind.
+ apply (le_to_not_lt ? ? ? H1).
+ apply le_O_n
+ |intros.simplify.
+ apply lt_times_r1
+ [apply (trans_lt ? (S O))[apply le_n|assumption]
+ |apply H
+ [apply H1
+ |apply le_S_S_to_le.assumption
+ ]
+ ]
+ ]
+qed.
+
+theorem lt_exp1: \forall n,m,p:nat. O < p \to n < m \to exp n p < exp m p.
+intros.
+elim H
+ [rewrite < exp_n_SO.rewrite < exp_n_SO.assumption
+ |simplify.
+ apply lt_times;assumption
+ ]
+qed.
+
+theorem le_exp_to_le:
+\forall a,n,m. S O < a \to exp a n \le exp a m \to n \le m.
+intro.
+apply nat_elim2;intros
+ [apply le_O_n
+ |apply False_ind.
+ apply (le_to_not_lt ? ? H1).
+ simplify.
+ rewrite > times_n_SO.
+ apply lt_to_le_to_lt_times
+ [assumption
+ |apply lt_O_exp.apply lt_to_le.assumption
+ |apply lt_O_exp.apply lt_to_le.assumption
+ ]
+ |simplify in H2.
+ apply le_S_S.
+ apply H
+ [assumption
+ |apply (le_times_to_le a)
+ [apply lt_to_le.assumption|assumption]
+ ]
+ ]
+qed.
+
+theorem le_exp_to_le1 : \forall n,m,p.O < p \to exp n p \leq exp m p \to n \leq m.
+intros;apply not_lt_to_le;intro;apply (lt_to_not_le ? ? ? H1);
+apply lt_exp1;assumption.
+qed.
+
+theorem lt_exp_to_lt:
+\forall a,n,m. S O < a \to exp a n < exp a m \to n < m.
+intros.
+elim (le_to_or_lt_eq n m)
+ [assumption
+ |apply False_ind.
+ apply (lt_to_not_eq ? ? H1).
+ rewrite < H2.
+ reflexivity
+ |apply (le_exp_to_le a)
+ [assumption
+ |apply lt_to_le.
+ assumption
+ ]
+ ]
+qed.
+
+theorem lt_exp_to_lt1:
+\forall a,n,m. O < a \to exp n a < exp m a \to n < m.
+intros.
+elim (le_to_or_lt_eq n m)
+ [assumption
+ |apply False_ind.
+ apply (lt_to_not_eq ? ? H1).
+ rewrite < H2.
+ reflexivity
+ |apply (le_exp_to_le1 ? ? a)
+ [assumption
+ |apply lt_to_le.
+ assumption
+ ]
+ ]
+qed.
+
+theorem times_exp:
+\forall n,m,p. exp n p * exp m p = exp (n*m) p.
+intros.elim p
+ [simplify.reflexivity
+ |simplify.
+ rewrite > assoc_times.
+ rewrite < assoc_times in ⊢ (? ? (? ? %) ?).
+ rewrite < sym_times in ⊢ (? ? (? ? (? % ?)) ?).
+ rewrite > assoc_times in ⊢ (? ? (? ? %) ?).
+ rewrite < assoc_times.
+ rewrite < H.
+ reflexivity
+ ]
+qed.
+
+theorem monotonic_exp1: \forall n.
+monotonic nat le (\lambda x.(exp x n)).
+unfold monotonic. intros.
+simplify.elim n
+ [apply le_n
+ |simplify.
+ apply le_times;assumption
+ ]
+qed.
+
+
+
\ No newline at end of file
projects / helm.git / blobdiff