Dear all, I think I have found a bug in maxima I have entered the following commands: reset();kill(all); assume(z>r); radcan(sqrt(r^2-2*z*r+z^2)); it gives z-r works fine but with capital R reset();kill(all); assume(z>R); radcan(sqrt(R^2-2*z*R+z^2)); it gives R-z should be z-R z-r Sincerely Rubens Marinho