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 4 x 4 + a 3 x 3 + a 2 x 2 + a 1 x + a 0 {\displaystyle y^{2}=a_{4}x^{4}+a_{3}x^{3}+a_{2}x^{2}+a_{1}x+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.
References Birch, Bryan (2004), "Heegner points: the beginnings", in Darmon, Henri; Zhang, Shou-Wu (eds.), Heegner points and Rankin L-series, Math. Sci. Res. Inst. Publ., vol. 49, Cambridge University Press, pp. 1–10, CiteSeerX 10.1.1.231.4662, doi:10.1017/CBO9780511756375.002, ISBN 978-0-521-83659-3, MR 2083207 {{citation}}: Cite uses deprecated parameter |citeseerx= (help)