Let <I>F</i> be a field and
 <i>f</i>(<i>x</i>)  a nonconstant polynomial
in <I>F</I>[<I>x</I>].
Then there is an extension field <I>E</i> of <I>F</i> in which
 <i>f</i>(<i>x</i>)
 has a zero.