| 释义 |
iff
A written form of abbreviation of the phrase ‘if and only if’, always read as ‘if and only if’, used in Math. and Logic to introduce a condition that is necessary as well as sufficient, or a statement that is implied by and implies the preceding one.
1955J. L. Kelley Gen. Topology vii. 232 F is equicontinuous at x iff there is a neighborhood of x whose image under every member of F is small. 1961R. R. Stoll Sets, Logic, & Axiomatic Theories i. 5 Two sets are equal iff (if and only if) they have the same members. 1964T. O. Moore Elem. Gen. Topol. i. 2 We use ‘iff’ as an abbreviation for ‘if and only if’. 1965B. Mates Elem. Logic viii. 137 ϕ {elem} Δ iff ϕ is derivable from Δ. 1971G. Hunter Metalogic 16 Hereafter we abbreviate ‘if and only if’ to ‘iff’. 1972R. Inst. Philos. Lect. V. 34 An integer n is prime iff the only integers which divide it without remainder are itself and one. |