integrate returns 0

Hello all,

I'm trying to check a property of so-called 'Koornwinder-Dubiner'
polynomials.  According to

http://www.springerlink.com/content/1l4h576r307l62n6/

they are defined over the reference triangle {r,s>=-1 and r+s <= 0} as

  a:2*(1+r)/(1-s)-1;
  b:s;
  psi(r,s):=sqrt((2*i+1)*(i+j+1)/2)*jacobi_p(i,0,0,a)*((1-s)/2)^i*jacobi_p(j,2*i+1,0,b);

for certain i and j.  According to the literature, these
polynomials are orthonormal with respect to the L2-norm over
the reference triangle, so I compute (i choose i=j=1):

  i:1;
  j:1;
  integrate(integrate((psi(r,s))^2, r, -1, -s), s, -1, -1);

and maxima returns 0 for the result of this integral, which is
not what I expect for a polynomial that is orthonormal.  I would
expect 1 there.

Is maxima giving me a wrong answer here, or am I misunderstanding
something?

Regards,
Bart

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