LIB "difform.lib";
ring R = 17,(a,b,c),lp;
diffAlgebra();
==> // The differential algebra Omega_R was constructed and the differential \
   forms dDa, dDb, dDc, da, db, dc are available.
list L = "",3,12*a,da-db,16 + dc, 23*da - 4*db*dc*da, db - 4, "entry", dc - db*da, a;
//////////////////////////
// Elements in the list //
//////////////////////////
difformListCont(L,da - db);
==> 1
difformListCont(L,16 + dc);
==> 1
difformListCont(L,dc - db*da);
==> 1
//////////////////////////////
// Elements not in the list //
//////////////////////////////
difformListCont(L,22*da);
==> 0
difformListCont(L,1);
==> 0
difformListCont(L,a);
==> 0
kill Omega_R,L,da,db,dc;