1 (**************************************************************************)
4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| The HELM team. *)
8 (* ||A|| http://helm.cs.unibo.it *)
10 (* \ / This file is distributed under the terms of the *)
11 (* v GNU General Public License Version 2 *)
13 (**************************************************************************)
15 set "baseuri" "cic:/matita/algebra/groups/".
17 include "algebra/monoids.ma".
18 include "nat/le_arith.ma".
20 record isGroup (M:Monoid) (opp: M -> M) : Prop ≝
21 { opp_is_left_inverse: is_left_inverse M opp;
22 opp_is_right_inverse: is_right_inverse M opp
27 opp: monoid -> monoid;
28 group_properties: isGroup ? opp
31 coercion cic:/matita/algebra/groups/monoid.con.
36 interpretation "Monoid coercion" 'monoid G =
37 (cic:/matita/algebra/groups/monoid.con G).
40 for @{ 'type_of_group $G }.
42 interpretation "Type_of_group coercion" 'type_of_group G =
43 (cic:/matita/algebra/groups/Type_of_Group.con G).
46 for @{ 'semigroup_of_group $G }.
48 interpretation "Semigroup_of_group coercion" 'semigroup_of_group G =
49 (cic:/matita/algebra/groups/SemiGroup_of_Group.con G).
51 notation "hvbox(x \sup (-1))" with precedence 89
54 interpretation "Group inverse" 'gopp x =
55 (cic:/matita/algebra/groups/opp.con _ x).
57 definition left_cancellable ≝
58 λT:Type. λop: T -> T -> T.
59 ∀x. injective ? ? (op x).
61 definition right_cancellable ≝
62 λT:Type. λop: T -> T -> T.
63 ∀x. injective ? ? (λz.op z x).
65 theorem eq_op_x_y_op_x_z_to_eq:
66 ∀G:Group. left_cancellable G (op G).
68 unfold left_cancellable;
71 rewrite < (e_is_left_unit ? ? (monoid_properties G));
72 rewrite < (e_is_left_unit ? ? (monoid_properties G) z);
73 rewrite < (opp_is_left_inverse ? ? (group_properties G) x);
74 rewrite > (semigroup_properties G);
75 rewrite > (semigroup_properties G);
81 theorem eq_op_x_y_op_z_y_to_eq:
82 ∀G:Group. right_cancellable G (op G).
84 unfold right_cancellable;
86 simplify;fold simplify (op G);
88 rewrite < (e_is_right_unit ? ? (monoid_properties G));
89 rewrite < (e_is_right_unit ? ? (monoid_properties G) z);
90 rewrite < (opp_is_right_inverse ? ? (group_properties G) x);
91 rewrite < (semigroup_properties G);
92 rewrite < (semigroup_properties G);
98 record finite_enumerable (T:Type) : Type ≝
102 index_of_sur: ∀x.index_of x ≤ order;
103 index_of_repr: ∀n. n≤order → index_of (repr n) = n;
104 repr_index_of: ∀x. repr (index_of x) = x
107 notation < "hvbox(C \sub i)" with precedence 89
108 for @{ 'repr $C $i }.
110 interpretation "Finite_enumerable representation" 'repr C i =
111 (cic:/matita/algebra/groups/repr.con C _ i).
113 notation < "hvbox(|C|)" with precedence 89
116 interpretation "Finite_enumerable order" 'card C =
117 (cic:/matita/algebra/groups/order.con C _).
120 ∀T:Type. ∀H:finite_enumerable T.
121 ∀n,n'. n ≤ order ? H → n' ≤ order ? H →
122 repr ? H n = repr ? H n' → n=n'.
124 rewrite < (index_of_repr ? ? ? H1);
132 finite_enumerable (carrier G) →
133 left_cancellable (carrier G) (op G) →
134 right_cancellable (carrier G) (op G) →
137 letin f ≝ (λn.index_of ? H ((repr ? H O)·(repr ? H n)));
138 cut (∀n.n ≤ order ? H → ∃m.f m = n);
139 [ letin EX ≝ (Hcut O ?);
145 letin HH ≝ (eq_f ? ? (repr ? H) ? ? H3);
147 rewrite > (repr_index_of ? H) in HH;
148 apply (ex_intro ? ? (repr ? H a));
149 letin GOGO ≝ (refl_eq ? (repr ? H O));
151 rewrite < HH in GOGO;
152 rewrite < HH in GOGO:(? ? % ?);
153 rewrite > (semigroup_properties G) in GOGO;
154 letin GaGa ≝ (H1 ? ? ? GOGO);
158 [ unfold is_left_unit; intro;
159 letin GaxGax ≝ (refl_eq ? ((repr ? H a)·x));
161 rewrite < GaGa in GaxGax:(? ? % ?);
162 rewrite > (semigroup_properties G) in GaxGax;
163 apply (H1 ? ? ? GaxGax)
164 | unfold is_right_unit; intro;
165 letin GaxGax ≝ (refl_eq ? (x·(repr ? H a)));
167 rewrite < GaGa in GaxGax:(? ? % ?);
168 rewrite < (semigroup_properties G) in GaxGax;
169 apply (H2 ? ? ? GaxGax)