The problem is evident: we did not keep track of the equality relationship between x and y; actually, this domain of intervals does not take into account any relationships between variables, and is thus a non-relational domain.
问题是显然的: 我们不跟踪在 x 和 y 之间的相等关系；实际上，这个区间的域不考虑在变量间的任何关系，因此是非关联域。