Hello,

first of all thanks a lot for the tip with unapply and especially to John for the running examples, that helped a lot.
Everything works fine now. :-)

A question so: Whats wrong with indexed variables? Is there an advantage of useing x_i instead of x[i]?
(I realize that John used the underscore instead of the index to get the substitutions right but Axel mentioned that
there are some troubles with indexed variables)

Greetings, Christian