X-Git-Url: http://matita.cs.unibo.it/gitweb/?p=helm.git;a=blobdiff_plain;f=matita%2Flibrary%2Fnat%2Fsigma_and_pi.ma;fp=matita%2Flibrary%2Fnat%2Fsigma_and_pi.ma;h=10727ed3ee492295f1e2414dc49bb2c548624532;hp=0000000000000000000000000000000000000000;hb=f61af501fb4608cc4fb062a0864c774e677f0d76;hpb=58ae1809c352e71e7b5530dc41e2bfc834e1aef1

diff --git a/matita/library/nat/sigma_and_pi.ma b/matita/library/nat/sigma_and_pi.ma
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+(**************************************************************************)
+(*       ___	                                                            *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||       A.Asperti, C.Sacerdoti Coen,                          *)
+(*      ||A||       E.Tassi, S.Zacchiroli                                 *)
+(*      \   /                                                             *)
+(*       \ /        Matita is distributed under the terms of the          *)
+(*        v         GNU Lesser General Public License Version 2.1         *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "nat/factorial.ma".
+include "nat/exp.ma".
+include "nat/lt_arith.ma".
+
+let rec sigma n f m \def
+  match n with 
+  [ O \Rightarrow (f m)
+  | (S p) \Rightarrow (f (S p+m))+(sigma p f m)].
+
+let rec pi n f m \def
+  match n with 
+  [ O \Rightarrow f m
+  | (S p) \Rightarrow (f (S p+m))*(pi p f m)].
+  
+theorem eq_sigma: \forall f,g:nat \to nat.
+\forall n,m:nat.
+(\forall i:nat. m \le i \to i \le m+n \to f i = g i) \to
+(sigma n f m) = (sigma n g m).
+intros 3.elim n.
+simplify.apply H.apply le_n.rewrite < plus_n_O.apply le_n.
+simplify.
+apply eq_f2.apply H1.
+change with (m \le (S n1)+m).apply le_plus_n.
+rewrite > (sym_plus m).apply le_n.
+apply H.intros.apply H1.assumption.
+rewrite < plus_n_Sm.
+apply le_S.assumption.
+qed.
+
+theorem eq_pi: \forall f,g:nat \to nat.
+\forall n,m:nat.
+(\forall i:nat. m \le i \to i \le m+n \to f i = g i) \to
+(pi n f m) = (pi n g m).
+intros 3.elim n.
+simplify.apply H.apply le_n.rewrite < plus_n_O.apply le_n.
+simplify.
+apply eq_f2.apply H1.
+change with (m \le (S n1)+m).apply le_plus_n.
+rewrite > (sym_plus m).apply le_n.
+apply H.intros.apply H1.assumption.
+rewrite < plus_n_Sm.
+apply le_S.assumption.
+qed.
+
+theorem eq_fact_pi: \forall n. (S n)! = pi n (\lambda m.m) (S O).
+intro.elim n.
+simplify.reflexivity.
+change with ((S(S n1))*(S n1)! = ((S n1)+(S O))*(pi n1 (\lambda m.m) (S O))).
+rewrite < plus_n_Sm.rewrite < plus_n_O.
+apply eq_f.assumption.
+qed.
+
+theorem exp_pi_l: \forall f:nat\to nat.\forall n,m,a:nat.
+(exp a (S n))*pi n f m= pi n (\lambda p.a*(f p)) m.
+intros.elim n.simplify.rewrite < times_n_SO.reflexivity.
+simplify.
+rewrite < H.
+rewrite > assoc_times. 
+rewrite > assoc_times in\vdash (? ?  ? %).
+apply eq_f.rewrite < assoc_times. 
+rewrite < assoc_times. 
+apply eq_f2.apply sym_times.reflexivity.
+qed.