def p_alg_op(p):
    """alg_op : expr PLUS expr
               | expr MINUS expr
               | expr MULTIPLY expr
               | expr DIVIDE expr"""
    if p[2] == '+':
        p[0] = 'addition', p[1], p[3]
    elif p[2] == '-':
        p[0] = 'subtraction', p[1], p[3]
    if p[2] == '*':
        p[0] = 'multiply', p[1], p[3]
    if p[2] == '/':
        p[0] = 'divide', p[1], p[3]
