A Lindenmayer system, also known as an L-system, is a parallel string rewriting system. It consists of an alphabet, an
initial string called the axiom, and production rules. At each step, all symbols
in the current string are replaced simultaneously according to the rules (Prusinkiewicz
and Lindenmayer 1990, pp. 3-4). Lindenmayer (1968a, 1968b) introduced these
systems to model cellular development.
In a simple deterministic example, the axiom is and the rule is . Interpreting as a forward step and and as turns through gives successive approximations to the Koch
curve. Symbols without a specified rule, such as the turn symbols, remain unchanged.
The geometric interpretation is separate from the rewriting rules (Prusinkiewicz
and Lindenmayer 1990, pp. 6-8). Several fractals
generated using Lindenmayer systems are illustrated above.