Solving Thue equations without the full unit group

The main problem when solving a Thue equation is the computation of the unit group of a certain number field. It is shown that the knowledge of a subgroup of finite index is in fact sufficient. Two examples linked with the primitive divisor problem for Lucas and Lehmer sequences are given. || La principale difficulte lors de la resolution d'une equation de Thue reside dans le calcul du groupe des unites du corps de nombres associe. On montre qu'il suffit en fait de connaitre un sous-groupe d'indice fini de ce groupe. On donne deux exemples li

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