de a^23=b(mod 91), on tire b^23=a^(23^2) (mod 91), or 23^2=1+48k (pour un certain k), d'où a^(23^2)=a^(1+48*k)=a*a^(48*k)=a*1=a(mod 91) car a^48=1(mod 91), d'où a^(48*k)=1(mod 91).
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Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe