The Flory-Wall expressions for the fraction of substituents remaining on a vinyl copolymer, when substituents are removed at random from adjacent 1,3 positions, are extended to the case of nonrandom copolymerization. A copolymer composition equation is derived for the case in which the type of monomer preceding the active free-radical chain end affects the propagation reaction. The distribution of lengths of sequences in copolymers is discussed.