1 (**************************************************************************)
4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| A.Asperti, C.Sacerdoti Coen, *)
8 (* ||A|| E.Tassi, S.Zacchiroli *)
10 (* \ / Matita is distributed under the terms of the *)
11 (* v GNU Lesser General Public License Version 2.1 *)
13 (**************************************************************************)
15 set "baseuri" "cic:/matita/nat/minimization".
17 include "nat/minus.ma".
18 include "datatypes/bool.ma".
26 | (S j) \Rightarrow max j f ]].
28 theorem max_O_f : \forall f: nat \to bool. max O f = O.
35 theorem max_S_max : \forall f: nat \to bool. \forall n:nat.
36 (f (S n) = true \land max (S n) f = (S n)) \lor
37 (f (S n) = false \land max (S n) f = max n f).
38 intros.simplify.elim (f (S n)).
39 simplify.left.split.reflexivity.reflexivity.
40 simplify.right.split.reflexivity.reflexivity.
43 definition max_spec \def \lambda f:nat \to bool.\lambda n: nat.
44 ex nat (\lambda i:nat. (le i n) \land (f i = true)) \to
45 (f n) = true \land (\forall i. i < n \to (f i = false)).
47 theorem f_max_true : \forall f:nat \to bool. \forall n:nat.
48 ex nat (\lambda i:nat. (le i n) \land (f i = true)) \to f (max n f) = true.
50 elim n.elim H.elim H1.generalize in match H3.
51 apply le_n_O_elim a H2.intro.simplify.rewrite > H4.
54 apply bool_ind (\lambda b:bool.
55 (f (S n1) = b) \to (f ([\lambda b:bool.nat] match b in bool with
56 [ true \Rightarrow (S n1)
57 | false \Rightarrow (max n1 f)])) = true) ? ? ?.
59 simplify.intro.assumption.
60 simplify.intro.apply H.
61 elim H1.elim H3.generalize in match H5.
62 apply le_n_Sm_elim a n1 H4.
64 apply ex_intro nat ? a.
65 split.apply le_S_S_to_le.assumption.assumption.
66 intros.apply False_ind.apply not_eq_true_false ?.
67 rewrite < H2.rewrite < H7.rewrite > H6. reflexivity.
70 theorem lt_max_to_false : \forall f:nat \to bool.
71 \forall n,m:nat. (max n f) < m \to m \leq n \to f m = false.
73 elim n.absurd le m O.assumption.
74 cut O < m.apply lt_O_n_elim m Hcut.exact not_le_Sn_O.
75 rewrite < max_O_f f.assumption.
76 generalize in match H1.
77 (* ?? non posso generalizzare su un goal implicativo ?? *)
80 absurd m \le S n1.assumption.
81 apply lt_to_not_le.rewrite < H6.assumption.
83 apply le_n_Sm_elim m n1 H2.
85 apply H.rewrite < H6.assumption.
86 apply le_S_S_to_le.assumption.
87 intro.rewrite > H7.assumption.
90 let rec min_aux off n f \def
92 [ true \Rightarrow (n-off)
96 | (S p) \Rightarrow min_aux p n f]].
98 definition min : nat \to (nat \to bool) \to nat \def
99 \lambda n.\lambda f. min_aux n n f.
101 theorem min_aux_O_f: \forall f:nat \to bool. \forall i :nat.
103 intros.simplify.rewrite < minus_n_O.
105 simplify.reflexivity.
106 simplify.reflexivity.
109 theorem min_O_f : \forall f:nat \to bool.
111 intro.apply min_aux_O_f f O.
114 theorem min_aux_S : \forall f: nat \to bool. \forall i,n:nat.
115 (f (n -(S i)) = true \land min_aux (S i) n f = (n - (S i))) \lor
116 (f (n -(S i)) = false \land min_aux (S i) n f = min_aux i n f).
117 intros.simplify.elim (f (n - (S i))).
118 simplify.left.split.reflexivity.reflexivity.
119 simplify.right.split.reflexivity.reflexivity.
122 theorem f_min_aux_true: \forall f:nat \to bool. \forall off,m:nat.
123 ex nat (\lambda i:nat. (le (m-off) i) \land (le i m) \land (f i = true)) \to
124 f (min_aux off m f) = true.
126 elim off.elim H.elim H1.elim H2.
128 rewrite > min_aux_O_f f.rewrite < Hcut.assumption.
129 apply antisym_le a m .assumption.rewrite > minus_n_O m.assumption.
131 apply bool_ind (\lambda b:bool.
132 (f (m-(S n)) = b) \to (f ([\lambda b:bool.nat] match b in bool with
133 [ true \Rightarrow m-(S n)
134 | false \Rightarrow (min_aux n m f)])) = true) ? ? ?.
136 simplify.intro.assumption.
137 simplify.intro.apply H.
138 elim H1.elim H3.elim H4.
139 elim (le_to_or_lt_eq (m-(S n)) a H6).
140 apply ex_intro nat ? a.
142 apply lt_minus_S_n_to_le_minus_n.assumption.
143 assumption.assumption.
144 absurd f a = false.rewrite < H8.assumption.
146 apply not_eq_true_false.
149 theorem lt_min_aux_to_false : \forall f:nat \to bool.
150 \forall n,off,m:nat. (n-off) \leq m \to m < (min_aux off n f) \to f m = false.
152 elim off.absurd le n m.rewrite > minus_n_O.assumption.
153 apply lt_to_not_le.rewrite < min_aux_O_f f n.assumption.
154 generalize in match H1.
155 elim min_aux_S f n1 n.
157 absurd n - S n1 \le m.assumption.
158 apply lt_to_not_le.rewrite < H6.assumption.
160 elim le_to_or_lt_eq (n -(S n1)) m.
161 apply H.apply lt_minus_S_n_to_le_minus_n.assumption.
162 rewrite < H6.assumption.assumption.
163 rewrite < H7.assumption.
166 theorem le_min_aux : \forall f:nat \to bool.
167 \forall n,off:nat. (n-off) \leq (min_aux off n f).
169 elim off.rewrite < minus_n_O.
170 rewrite > min_aux_O_f f n.apply le_n.
171 elim min_aux_S f n1 n.
172 elim H1.rewrite > H3.apply le_n.
173 elim H1.rewrite > H3.
174 apply trans_le (n-(S n1)) (n-n1) ?.
175 apply monotonic_le_minus_r.