def p_binary_expression_3(self, p):
    ' expression  : expression CONSTRAINT_OP LBRACE constraint_list RBRACE '
    p[0] = ConstraintSymbol(p[1], p[4])
expression  : expression CONSTRAINT_OP LBRACE constraint_list RBRACE
def p_binary_expression_3(self, p):
    '  '
    p[0] = ConstraintSymbol(p[1], p[4])