(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
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(*                 The Calculus of Inductive Constructions                  *)
(*                                                                          *)
(*                                Projet Coq                                *)
(*                                                                          *)
(*                     INRIA                        ENS-CNRS                *)
(*              Rocquencourt                        Lyon                    *)
(*                                                                          *)
(*                                Coq V5.10                                 *)
(*                              Nov 25th 1994                               *)
(*                                                                          *)
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(*                                 groups.v                                 *)
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Require Export Lci.
Require Export misc.
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Section groups.
Variable S : Set.
Variable G : S -> Prop.
Variable Add : S -> S -> S.
Variable O : S.
Variable Opp : S -> S.
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Definition is_group :=
intern S G Add /\
associativity S Add /\ neutral S G Add O /\ opposite S G Add O Opp.

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Lemma opp_opp : is_group -> forall x : S, G x -> x = Opp (Opp x).