public @Nullable RelationType meet(@NotNull RelationType other) {
    if (isSubRelation(other)) return other;
    if (other.isSubRelation(this)) return this;
    if (this == NE && other == LE || this == LE && other == NE) return LT;
    if (this == NE && other == GE || this == GE && other == NE) return GT;
    if (this == LE && other == GE || this == GE && other == LE) return EQ;
    return null;
  }
public @Nullable RelationType meet(@NotNull RelationType other)