What does $g \to \lambda$ mean in the L-System for the dragon curve?

I am playing with L-System using the wonderful tool jflap. Below is the L-System for the dragon curve in the "JFLAP book: JFLAP – An Interactive Formal Languages and Automata Package " (you can find it in the left column of its homepage).

What does the third rewriting rule "$$g \to \lambda$$" mean? I did not find any references.

1 Answer

"$$\lambda$$" is commonly used to represent the empty string, although "$$\epsilon$$" could be the more common one.

This was introduced earlier in that book, section "3.1 Grammar Editing" of chapter "Regular Grammars".

On the last row you will enter the production $$A \rightarrow \lambda$$, a $$\lambda$$-production. To do this, enter $$A$$ into the left cell, but leave the right cell blank. The right field is really empty, but will display with a $$\lambda$$ to signify that it is a $$\lambda$$-production.

In the case of $$\text{L}$$-system, a $$\lambda$$-production rewriting rule means the symbol on the left will be gone in the next iteration.