Найти предел с двумя переменными: (x,y -> 1,1). Lim x-y/x^2-y^2

(x-y)/(x^2-y^2) = (x-y)/((x-y)*(x+y)) = 1/(x+y);
lim(x,y->1) 1/(x+y) = 1/2;

lim(y->1) lim(x->1) (x-y)/(x^2-y^2) = lim(y->1) (1-y)/(1-y^2) = lim(y->1) 1/(1+y) = 1/2;

lim(x->1) lim(y->1) (x-y)/(x^2-y^2) = lim(x->1) (x-1)/(x^2-1) = lim(x->1) 1/(x+1) =
1/2