9. To adopt the practice that the denominator of a fraction be positive (numerator may be negative or zero),
the set of rational numbers may be built by Q = { me Zane N). Consider each rule from Q to Z.
Use fractions to verify the underlined statement (show by example).
a. Let r(m/n) = mn. Then r is not well-defined: the relation r defined by (m/n, mn) er is not a fetn;
that is, the relation r on Q x Z via xry (y=mn VmeZAneNo: x=m/n) is not a function.