A prime ideal <i>A</i> of a commutative ring <i> R</I> 
is a proper ideal of <I> R</I> such that, <I>a, b </I> in  <I>R </I> and <I>ab</I> in  <I>A </I> 
imply that <I>a </I> is in  <i>A </i> or <i>b</I> is in <i> A </i>.