ABSTRACT
An EW matrix exists only if 2n − 2 is a sum of two squares. It is not known whether equality in (4) of Theorem 3.8 ever holds.
3.10 Theorem Let A, B be circulant (±1)-matrices of order n/2 with AAt + BBt = (n− 2)In/2 + 2Jn/2. Then there is an Ehlich matrix of order n.
