LIB "difform.lib";
ring R = 0,(x,y,z),ds;
diffAlgebra();
==> // The differential algebra Omega_R was constructed and the differential \
   forms dDx, dDy, dDz, dx, dy, dz are available.
///////////////////////////////////////
// Subtraction of differential forms //
///////////////////////////////////////
difform df = 5*dx*x2 - 7*dy*z - 2x2*dz - 3;
difform dg = dx - 8x*dz*dy;
df-dg;
==> -3+(-1+5x2)*dx+(-7z)*dy+(-2x2)*dz+(-8x)*dy*dz
==> 
///////////////////////////////////////////////////////
// Subtraction of polynomials and differential forms //
///////////////////////////////////////////////////////
df - 2x3;
==> -3-2x3+5x2*dx+(-7z)*dy+(-2x2)*dz
==> 
1 - dg;
==> 1+(-1)*dx+(-8x)*dy*dz
==> 
kill Omega_R,df,dg,dx,dy,dz;