Closure
Let a,b ∈U(n).
a has no common factor with n (other than 1)
b has no common factor with n(,,)
So,
If ab < n, then ab doesn't have any common factors with n.
If ab>n, then for some p,ab-pn < n.
Since ab doesn't have any common factor with n, ab-pn can't either.
(ab≠ n, because neither a...