Chomsky Normal Form

What

It’s a subset of Context-Free Language with 3 strict requirements. They are:

1. $A$ → $BC$ (two non-terminals)
2. $A$ → $a$ (a single terminal)
3. $A$ → $ϵ$ (empty string)

Why bother?

Well it turns out any legal production ruleset of a Language (specifically Context-Free Language) can be transformed into CNF. Then we can apply the CYK Algorithm to turn a sentence into a tree using the CNF version of it.