We have a function f: R^2->R, f(x,y) := 2*exp(-x-y) if 0<x<y and f(x,y) := 0 otherwise (the blue set is where f is NOT 0)
Let M := {(x,y) in R^2 | x<2y} (the green set)

TASK:
Calculate: integral of f(x,y) over M