"Or" and "He" are important related words in mathematics, and they are very different! Don't mix together! Every teacher will emphasize this point! "Or" indicates a coordinate relationship; "He" means both. For example: ab = 0. So, a=0 or b=0. ab ≠ 0。 Then, a≠0, b≠0. The "and" here must not be "or". A word difference, a thousand miles difference! In high school, "or" means merger; "Harmony" means repetition. In the set: "or" means union; "He" means intersection.