#5229 Variables a and z leak into derivative of gamma_incomplete

[David Scherfgen]

(%i1) a : foo$ z : bar$ assume(b > 0)$

(%i2) diff(gamma_incomplete(b, y), b);
(%o2) bar^foo*gamma(foo)^2*hypergeometric_regularized([foo,foo],[foo+1,foo+1],-bar)+log(bar)*(gamma_incomplete(foo,bar)-gamma(foo))+psi[0](foo)*gamma(foo)

The foo and bar in the derivative comes from the variables a and z, which don't even occur in the expression that's being differentiated.

[Raymond Toy]

A note. The assume(b>0) is important. Without it, you just get the noun form for the derivative.

[David Scherfgen]

I have a fix ready using mbinding.

[David Scherfgen]

Fixed by commit [9cca9a].