(VAR X Y DX DY DDX)
(RULES

din(der(plus(X,Y))) -> u21(din(der(X)),X,Y)
u21(dout(DX),X,Y) -> u22(din(der(Y)),X,Y,DX)
u22(dout(DY),X,Y,DX) -> dout(plus(DX,DY))
din(der(times(X,Y))) -> u31(din(der(X)),X,Y)
u31(dout(DX),X,Y) -> u32(din(der(Y)),X,Y,DX)
u32(dout(DY),X,Y,DX) -> dout(plus(times(X,DY),times(Y,DX)))
din(der(der(X))) -> u41(din(der(X)),X)
u41(dout(DX),X) -> u42(din(der(DX)),X,DX)
u42(dout(DDX),X,DX) -> dout(DDX)


)