Solution
= Solution
A <context-free grammar> is in <Chomsky normal form> when every <production rule> has one of the forms
$$
A\to BC,\qquad A\to a,
$$
where $A,B,C$ are <nonterminal symbols> and $a$ is a <terminal symbol>. If the language contains the <empty word>, one may additionally permit $S_0\to\epsilon$, with the start symbol $S_0$ absent from all right-hand sides.