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construction: centemaispasd'exhibersabase.Lelemmesuivantvanouspermettred'eectuerla 48Lapreuveprecedentenouspermetd'armerl'existencedel'enveloppeadja-<br />

CHAPITRE3.THEOREMEDUDEFAUTETCODESNON-INT.<br />

Proposition3.1.3SoitXunepartiedeAetYlabasedesonenveloppeadjacente. Onaalorslesproprietessuivantes:<br />

x1;:::;xn2Y,y1;:::;ym2Y,w02P(Y)etk2[1;n]telsquex1:::xk=v, Preuve.Montronslapropriete(i). (ii)Pourtouslesmotsu2X,v2X+etw2S(X)telsqueu=wvonaw2Y. (i)Pourtouslesmotsu2X,v2X+etw2P(X)telsqueu=vwonaw2Y.<br />

xk+1:::xnw0=wety1:::ym=u.Deplus,onau=vwdonc Lelemme2.3.2assure,puisqueYestuncodeadjacent,quew02Ydoncw2Y. Comme,pardenitiondeY,onau;v2Y+etw2P(Y),ilexisten;m>1, x1:::xnw0=y1:::ym: u2Y+<br />

x1y1<br />

v2Y+ xk xk+1 w2P(Y) xnymw0<br />

lemotsuivant: Onraisonnedem^emepouretablirlapropriete(ii). PourtoutensemblenonvideCdeAettoutmotudeC,nousnoteronsPC(u) Fig.3.1{u=vw<br />

{Siu2C:C+alorsPC(u)=". <br />

{Sinon,PC(u)estlepluscourtmotnonvidewtelqueu2Cwetw2P(C) (ilestclairqu'untelmotexistepuisquelemotului-m^emeverieu2Cuet u2P(C)).

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