example18 := (-45+71*x^3+54*x^2*y+84*x^2-53*x*y^2+65*x*y-9*x+50*y^3-19*y^2-18* y)/(60-30*x^3+73*x^2*y-37*x^2+83*x*y^2-15*x*y-80*x-40*y^3+18*y^2+64*y)*((83+80 *x^2-33*x*y+67*x-14*y^2+82*y)/(-32+94*x^2+77*x*y+97*x-76*y^2+19*y))^(1/2)*exp( (63*x+16*y+7)/(-43*x-34*y-20));