EBNF: EXPRESSION = TERM, { ("+" | "-"), TERM } ; TERM = FACTOR, { ("*" | "/"), FACTOR } ; FACTOR = ("+" | "-") FACTOR | "(" EXPRESSION ")" | number ;

Obs: Since we consider every number a integer, we can abstract NUMER as: NUMBER = DIGIT, {DIGIT} ; DIGIT = 0 | 1 | ... | 9 ;