On relative integral bases for cyclic quartic fields
A necessary and sufficient condition for a cyclic quartic field to have an integral basis over its quadratic subfield is proved. However, such a necessary and sufficient condition has already been given by \textit{B. K. Spearman} and \textit{K. S. Williams} [Proc. Am. Math. Soc. 103, No.3, 687- 694 (1988; Zbl 0663.12006)].
scientific article; zbMATH DE number 4144080