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2.5.UNECARACTERISATIONDESCODESDEFdif dumonode,s2X.Ainsil'interpretation(s;y;p)dex2Xestquasi-trivialedonc, commeXestuncode,onas="oup=",cequicontredit(s;p)2S(X)P(X). Dem^eme,onnepeutavoirp:Xn\P(X)6=;. LecodeXveriedonclacondition(2.5). 39<br />

P(X)S(X)nXXtelsque lecodeXestdedelaid'interpretationauplusegala(n+1)(k+1). Montrons(ii))(i). Plusprecisementnousallonsmontrerquesousl'hypothesedelapropriete(ii), Supposonsqu'ilexisteq>0,x1;:::;x(n+1)(k+1)2X,y1;:::;yq2Xet(;)2<br />

(puisqu'onapris(;)=2XX).Maisdanscecas,l'equation2.6implique Remarquonsque=2Xet=2X.Eneet,si2X,onaalors=2X x1x2:::x(n+1)(k+1)=y1y2:::yq X+\(S(X)nX):X6=;: (2.6)<br />

CommeXestadjacent,lacondition(ii)delaproposition2.3.3assure Onadonc=x1:::x(n+1)(k+1)2Xcequicontredit=2X. g.2.2): Nousdenissonsl'applicationf:[0;q+1]7![0;(n+1)(k+1)]commesuit(cf. Onmontredem^emeque=2X. y1:::yq=":<br />

soitunprexedey1:::yj. f(q+1)=maxfi2[0;(n+1)(k+1)]jjx1:::xij6jy1:::yqjg Autrementdit,lenombref(j)estleplusgrandindicetelquelemotx1x2:::xf(j) f(0)=maxfi2[0;(n+1)(k+1)]jjx1:::xij6jjg<br />

Nouspouvonsalorsdenirlafonctiongpar: Ilestclairquef(p+1)=(n+1)(k+1)puisquejx1:::x(n+1)(k+1)j=jy1:::yqj. f(j)=maxfi2[0;(n+1)(k+1)]jjx1:::xij6jy1:::yjjg;j2[1;q]<br />

SoitI=f0g[f16i6q+1jf(i)6=f(i1)g.Pardenitiondeg,ona Xj2Ig(j)=q+1 g(0)=f(0) g(j)=f(j)f(j1)pour16j6q+1 Xj=0g(j)=f(q+1)=(n+1)(k+1):

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