Classical Lifroth theorem states that every subfield 1< of K(t), where t is a transcendental element over K, such that 1< stnictly contains K, must be 1< = K(h(t)), fon sorne non constant element hQ) e K(t). Therefore, E la K-isornorphic to K(t). This result can be proved with elementary algebraic techniques, and therefore it la usual!>’ included in basic courses on fleld theory or algebraic cu...
