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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.

dragon-rules

dragon

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"$\lambda$" 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.

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