Heegner's lemma

In mathematics, Heegner's lemma is a lemma used by Kurt Heegner in his paper on the class number problem. His lemma states that if
 * $$y^2=a_4x^4+a_3x^3+a_2x^2+a_1x+a_0 $$

is a curve over a field with a4 not a square, then it has a solution if it has a solution in an extension of odd degree.