The representation of binary quadratic forms by positive definite quaternary quadratic forms
A. G. Earnest · Transactions of the American Mathematical Society · 1994
A quadratic $\mathbb {Z}$-lattice L of rank n is denned to be k-regular for a positive integer $k \leq n$ if L globally represents all quadratic $\mathbb {Z}$-lattices of rank k which are represented everywhere locally by L. It is shown that there exist only finitely many isometry classes of primitive positive definite quadratic $\mathbb {Z}$-lattices of rank 4 which are 2-regular.