As a two-dimensional example, number X10Y20 denotes the Green's function in the quarter-infinite body ( 0 < x < ∞ ∞ , 0 < y < ∞ ∞ ) with a Dirichlet (type 1) boundary at x = 0 and a Neumann (type 2) boundary at y = 0. The boundary value problem for the X10Y20 Green's function is given by