>	a1(x,y):=exp(x/2)*exp(y)/2;

>	b1(x,y):=0.7/(x*x*y*y+0.5);

>	c1(x,y):=(4-exp(x)-exp(y/2))*2;

>	d1(x,y):=x*x+y;

>	e1(x,y):=x*y*y;

>	f1(x,y):=3*x+2*y;

>	u(x,y):=x*x*x+2*y*y*y+3*x*x*y+4*x*y*y+5*x*y+6*x+7*y+8;

>	ux(x,y):=diff(u(x,y),x);

>	uy(x,y):=diff(u(x,y),y);

>	uxy(x,y):=diff(ux(x,y),y);

>	uxx(x,y):=diff(ux(x,y),x);

>	uyy(x,y):=diff(uy(x,y),y);

>	c(x,y):=a1(x,y)*uxx(x,y)+b1(x,y)*uxy(x,y)+c1(x,y)*uyy(x,y)+d1(x,y)*ux(x,y)+e1(x,y)*uy(x,y)+f1(x,y);

>