Integrate[Integrate[Abs[Exp[2*Pi*I*x] + Exp[2*Pi*I*y]], {x, 0, 1}], {y, 0, 1}]
yields 0
as result.
This cannot be correct, because the integrand is positive and nonzero in the indicated region.
Wolfram Alpha sais: Standard computation time exceeded
, so I do not know if there the same comes out.
Any idea what is going on?