var(p) returns the list of all ring variables the arguments depends on.
Example:
ring r=0,(x,y,z),dp;
variables(2);
==> empty list
variables(x+y2);
==> [1]:
==> x
==> [2]:
==> y
variables(ideal(x+y2,x3y,z));
==> [1]:
==> x
==> [2]:
==> y
==> [3]:
==> z
string(variables(ideal(x+y2,x3y,z)));
==> x,y,z