Doug, Thanks a lot for the suggestion. Jean

Thanks a lot for the explanation. As I am not familiar with Mma your explanation is really useful. Regards, Jean

Dear Doug, Sandor, J. Tarr, Thanks a lot for the explantion.. your posts are more than sufficient to deal with my problem. Jean

After reading the answers I see now how to deal with my problem. Thanks a lot!! J

Thanks a lot for the comments. I think I would need to write a specific V(t) to work with MAPLE. I see that it is not possible to use an asssume command like "assume(V(t), real)". Maybe in next versions. Regards, JV