New Classes of Synchronous Codes

New classes of codes with similar application to Gilbert´s code [1] are defined. Weakening of his synchronizing condition gives higher efficiency in the new codes. One class (the F codes) is shown to be the most efficient possible among those codes which use Gilbert´s method of achieving synchronization, i.e., the ``position fixing´´ method. The other classes use a basically different method of achieving synchronization, and have even higher efficiencies than the F codes. The codes are compared mainly with regard to efficiency, but some idea of the hardware required is also given. The efficiency is compared to that of the bound on Golomb´s comma-free codes [2], but evidence is supplied that codes constructed to carry information will never reach this limit.