Add nsmallnqq and nsmallnq to iset.mm
Add nsmallnqq and nsmallnq to iset.mm

nsmallnq is stated as in set.mm . nsmallnqq is the same but also
asserts that the smaller value is a positive fraction. Proving
these in terms of halfnqq avoids the need for reverse closure.

metamath/set.mm,metamath/set.mm,metamath/set.mm