Are there any specific rules for intersection and union? Or or and, there is no rule. Determine whether to use or use and according to the meaning of the question. For example, to find a domain with a denominator, at this time, if the denominator is not equal to 0 under the condition that the numerator is meaningful, then "and" will be used. If the denominator is greater than 0, only the numerator is required to be meaningful.