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First of all, using less than < is bad practice for iterators, and from what I remember, list::iterator does not support it.
So use != instead: for ( nivel = arbolPaquetes.begin() ; nivel != (arbolPaquetes).end(); nivel++)
And then nivel, I think should be used as: for ( iteraPaquete = (*nivel).begin() ; iteraPaquete != (*nivel).end(); iteraPaquete++)