0 & lty & lt 1，y & ltx & lt 1

After drawing, change the order of integrals.

0 & ltx & lt 1，0 & lt； y & ltx

For e (x 2) integral, it only goes from 0 to infinity, which is mentioned in the book of high numbers.

Using γ function or double integral solution, the result is √π/2.

Others. . If it is encountered at present, it will definitely be eliminated.