On the Prime Ideals in a Commutative Ring

If $n$ and $m$ are positive integers, necessary and sufficient conditions are given for the existence of a finite commutative ring $R$ with exactly $n$ elements and exactly $m$ prime ideals. Next, assuming the Axiom of Choice, it is proved that if $R$ is a commutative ring and $T$ is a commutative $R$ -algebra which is generated by a set $I$ , then each chain of prime ideals of $T$ lying over the same prime ideal of $R$ has at most ${{2}^{\left| I \right|}}$ elements. A polynomial ring example shows that the preceding result is best-possible.