definite_integral(cos(y), y, 0, 3-x)
Instead of sin(3-x) it gives "ValueError: Computation failed since Maxima requested additional constraints; using the 'assume' command before evaluation may help (example of legal syntax is 'assume(x-3>0)', see assume? for more details) Is x-3 positive, negative or zero?"
When the lower bound is not 0 (1 or something else), everything works correctly.
What is the reason for this and how to fix it?
