Simplifying function taking some variables off.

OK:

x1(x2,x3):=x2+x3

f(x2,x3):=x1(x2,x3)+x2+x3

Would essentially become: f(x2,x3):=2*x2+2*x3

Then if (also): x2=x1+5*x3, it would mean that x2=x2+x3+5*x3, so 0=6*x3 and x3=0 and finally this means that

f is not a function of x3.

Does not make sense.

What exactly do you want?

Success!
Luc

If both condition have to be considered, as Liuc said, this would mean that x3=0 and x1=x2 and f(x2)=2*x2.

Even with other conditions - if you apply two independend conditions, f would only be dependent on one variable, not on two.

Here are two ways to do it with one condition - not sure if thats waht you are looking for: