(1+u) constacyclic and cyclic codes over F2+u F2

We introduce (1 + u) constacyclic and cyclic codes over the ring F-2 + u F-2 = {0, 1, u, = (u) over bar + 1}, where u(2) = 0, and study them by analogy with the Z(4) case. We prove that the Gray image of a linear (1 + u) constacyclic code over F-2 + u F-2 of length n is a binary distance invariant linear cyclic code. We also prove that, if n is odd, then every binary code which is the Gray image of a linear cyclic code over F-2 + uF(2) of length n is equivalent to a linear cyclic code. (C) 2005 Elsevier Ltd. All rights reserved.