Rewriting systems with a clocking mechanism

A new type of rewriting system is introduced in which every string in a derivation is preceded by one (clocking) symbol which must be rewritten at every moment of time, (hence in a parallel mode). The rest of the string is rewritten in a sequential mode, (i.e., one symbol at every moment of time). The communication from the clocking symbol to the rest of the string, and vice versa, is achieved by incorporating various types of context conditions in every production.