The integral invariants in the sense of Poincar6-Cartan refer to integral expressions in connection with the integral curves of a system of ordinary differential equations of first order in n variables. The object of this note is to generalize the notion of integral invariant to the integral varieties of a completely integrable system of Pfaff, as well as to extend to these varieties the integral relation of invariance given for the system of curves by Lichnerowicz [3],1 and other theorems

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... ding those relating to curves as particular cases. Some applications are given.