<letter> --> a | b | ... | y | z
ID --> <letter> +
<digit> --> 0 | 1 | ... | 9
NUMBER --> <digit>+
<reserved words> --> int | int2 | int10 | void | if | while | return | read | write
<symbols> --> left_parenthesis | right_parenthesis
| left_brace | right_brace | comma | semicolon
| plus_sign | minus_sign | star_sign | forward_slash
| == | != | > | >= | equal_sign
(The 15 symbols are: ( ) { } , ; + - * / == != > >= =)