\[ \newcommand{\tr}{\Rightarrow} \newcommand{\trs}{\tr^{\!\ast}} \newcommand{\rlnm}[1]{\mathsf{(#1)}} \newcommand{\rred}[1]{\xrightarrow{#1}} \newcommand{\rreds}[1]{\mathrel{\xrightarrow{#1}\!\!^*}} \newcommand{\cl}{\mathsf{Cl}} \newcommand{\pow}{\mathcal{P}} \newcommand{\matches}{\mathrel{\mathsf{matches}}} \newcommand{\kw}[1]{\mathsf{#1}} \newcommand{\andop}{\mathrel{\&\!\&}} \newcommand{\orop}{\mathrel{\|}} \newcommand{\ff}{\mathsf{false}} \newcommand{\tt}{\mathsf{true}} \newcommand{\abra}[1]{\langle #1 \rangle} \newcommand{\bnfnt}[1]{\abra{\small \textsf{#1}}} \newcommand{\llbracket}{[\![} \newcommand{\rrbracket}{]\!]} \newcommand{\first}{\mathsf{First}} \newcommand{\nullable}{\mathsf{Nullable}} \newcommand{\follow}{\mathsf{Follow}} \newcommand{\tm}[1]{\mathsf{#1}} \]

• An identifier, terminal $\mathsf{id}$, consists of a lowercase letter, which is followed by any number of upper or lowercase letters or the prime character (apostrophe).
• A number, terminal $\mathsf{num}$, consists of a non-empty sequence of digits.
• The while keyword, terminal $\mathsf{while}$, consists of the string “while”.
• A left parenthesis, terminal $\mathsf{lparen}$, consists of the single character ‘)’.
• The assignment symbol, terminal $\mathsf{assn}$, consists of the string “<-“.
• The plus symbol, terminal $\mathsf{plus}$, consists of the character ‘+’.
• and so on