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Thank you for your reply. I explained better the problem i would to solve in the post called "Can I treat indexed objects as variables?". I'll be glad if you can help me
I tried that but i can't do something like this Q[x_,a[k]_]:=V[x,a[k]+c]-V[x,a[k]]
Thank you for the reply. I made a mistake in the code i wrote, i know. However the problem remain: i had to take the only solution that is independent from L but i solve the problem writing ForAll[l,...] Thank you!