Excuse my very very bad english. I have a proble to compute integrate(acos(cos(t)),t,0,%pi/2), maxima return -3*%pi^2/8 instead of %pi^2/8. More genrally, it seems that for x in [0,%pi], maxima return x^2/2-%pi*x for integrate(acos(cos(t)),t,0,x) instead of x^2/2. Regards Paul Rey