olemus
üks ja ainult üks
(mitte näiteks kaks, mis samuti sisaldab üht)
=
one and not zero or two or any other number

ülevaateid
https://ell.stackexchange.com/questions/131671/only-one-vs-exactly-one-referring-item-count

http://mathworld.wolfram.com/ExactlyOne.html

https://en.wikipedia.org/wiki/Uniqueness_quantification

näiteid
https://image.slidesharecdn.com/introduction-to-postulates-and-theorems3009/95/introduction-to-postulates-and-theorems-5-728.jpg

http://images.slideplayer.com/39/10928646/slides/slide_2.jpg

https://image.slidesharecdn.com/introduction-to-postulates-and-theorems3009/95/introduction-to-postulates-and-theorems-13-728.jpg

https://www.toppr.com/ask/question/if-a-and-b-are-two-events-the-probability-that-exactly-one-of-them-occurs/

vt ka
- välistav VÕI (XOR)