# ZeroDiffOp -- the zero differential operator of a ring

## Description

For internal use. A type of DiffOp with a single key 1 and value 0. Users are not expected to create instances of ZeroDiffOp, they are created automatically by diffOp when necessary.

 i1 : R = QQ[x,y] o1 = R o1 : PolynomialRing i2 : D = diffOp{x => 0}; i3 : instance(D, ZeroDiffOp) o3 = true i4 : peek D o4 = ZeroDiffOp{1 => 0}

Comparison to the integer 0 works as expected

 i5 : E = diffOp{1_R => 0} o5 = 0 o5 : ZeroDiffOp i6 : E == 0 o6 = true