def p_constraint(self, p):
    ' constraint  : LBRACKET concrete_integer_expression COMMA concrete_integer_expression RBRACKET '
    p[0] = (p[2], p[4])
constraint  : LBRACKET concrete_integer_expression COMMA concrete_integer_expression RBRACKET
def p_constraint(self, p):
    '  '
    p[0] = (p[2], p[4])