(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
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(* This contribution was updated for Coq V5.10 by the COQ workgroup.        *)
(* January 1995                                                             *)
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(*      Coq V5.8                                                            *)
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(*      Alternating Bit Protocol                                            *)
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(*      Jan Friso Groote                                                    *)
(*      Utrecht University                                                  *)
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(*      November 1992                                                       *)
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(* From bezem@phil.ruu.nl Fri Apr  2 13:14:31 1993                          *)
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(*                                abp_lem2.v                                *)
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Theorem Lem1 : D + (fun d : D => seq (ia D r1 d) (X1 d)) = X.
unfold X at 1 in |- *.