text: Lewis's '"`UNIQ--postMath-00003C83-QINU`"' notation is still standard, but current practice usually takes its dual, '"`UNIQ--postMath-00003C84-QINU`"' ("necessity"), as primitive and '"`UNIQ--postMath-00003C85-QINU`"' as defined, in which case "A strictly implies B" is simply written as '"`UNIQ--postMath-00003C86-QINU`"'(A→B).