The problem with not and unless is double-negation, which is complex. I only use unless in postfix statement form, and I never use it if there's a not.

The problem with a negation and multiple conditionals is the same as in English -- ambiguity of the distributiveness of the negation. That's a case where parenthesizing helps.

In reply to Re^3: Useless unless by chromatic
in thread Useless unless by GrandFather

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