I'd like Maple to see that the derivative of p1 with respect to X includes p1 and p2

> p1 := exp(a*x)/(exp(a*x)+exp(b*x)+1);

> p2 := exp(b*x)/(exp(a*x)+exp(b*x)+1);
> m := eval(diff(p1, x));
> n := expand(m);
I see that algsubs won't work along the lines of

   algsubs(exp(a*x)/(exp(a*x)+exp(b*x)+1)=p1,n)

because the substitution is not a polynomial.

any other way to do this?

Boy, this program sure makes me feel like an idiot.  (I am a full professor at a top university, but maple has turned me into an idiot.)

so, here's my stupid question now:

(for those of you who do statistics, this is the principal stratification problem in causal inference.  Eventually, I'll replace equations 9-11 with other conditions.

I hope to show my class this.)

My actual problem is more complicated, but how do I get

     subs((x+1)^2 = a, (x+1)^6+2)

to look for transformations of the expression for which I'd like to substitute--

or

    subs((x+1)^2 = a, (x^2+2x+1)^3+2)

Perhaps this is just too much to expect.  Maple already blows my mind.  8-)