Type II codes over F/sub 4/

The natural analogues of Lee weight and Gray map over F/sub 4/ are introduced. Self-dual codes for the Euclidean scalar product with Lee weights multiples of 4 are called Type II. They produce Type II binary codes by Gray map. All extended Q-codes of length multiples of 4 are Type II, this includes generalized quadratic residue codes attached to a prime power q/spl equiv/7 (mod 8). Certain double circulant codes are also considered. The first binary extremal singly-even [92,46,16] self-dual code is constructed. A general mass formula is derived.