Variants of string assembling systems

Abstract String assembling systems are biologically inspired mechanisms that generate strings from copies out of finite sets assembly units. The underlying mechanism is based on piecewise a double-stranded sequence symbols, where the upper and lower strand have to match. generation additionally controlled by requirement first symbol unit has be same as last generated so far, well distinction units may appear at beginning, during, or end process length restriction We investigate power these model-inherent control considering variants one more relaxed. generative capacities relative our main interest. In particular, we prove gained in different yield strictly powerful incomparable capacities. Additionally, generalize multi-stranded systems. obtain strong connection one-way multi-head automata show an infinite, dense, strict hierarchy. Finally, examine closure properties string