iff
Abbreviation with 2 meanings
| Stands for | If and only if |
|---|---|
| Meanings | 2 |
| Categories | Units & Measurements, Military |
| Also written | IFF |
iff has two meanings. It stands for If and only if (math) or Identification friend or foe (military term).
Meanings of iff at a glance
| # | iff stands for | Context |
|---|---|---|
| 1 | If and only if | Units & Measurements › Math |
| 2 | Identification friend or foe | Military › Military Term |
1. If and only if
Units & Measurements · Math Abbreviations
Logical connective stating that two statements are equivalent, each implying the other. In "a number is even iff it is divisible by 2", both directions hold.
Example: A triangle is equilateral iff all three of its angles measure 60°.
Usually credited to mathematician Paul Halmos, who also popularized the tombstone symbol that ends a proof. It is written with two fs and read aloud as "if and only if". Symbols with the same meaning include ⇔ and ↔. Definitions often say "if" when they mean "iff", a convention that surprises many students.
2. Identification friend or foe (IFF)
Military · Military Term Abbreviations
Electronic system in which aircraft and ships automatically respond to interrogation signals with coded replies, allowing air defenses and pilots to distinguish friendly forces from potential threats.
Example: The fighter's IFF failed, so the controller ordered a visual identification.
Military IFF uses encrypted modes, and civil aircraft transponders descend from the same technology developed in World War II for radar. Failures of identification have contributed to friendly fire incidents. Pronounced as letters.
Related abbreviations
More math abbreviations
- GCD – Greatest common divisor
- GCF – Greatest common factor
- HCF – Highest common factor
- HL – Hypotenuse-Leg (congruence)
- Im – Imaginary part
- inf – Infimum
- IVT – Intermediate value theorem
- K – Thousand
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