Multisets are unordered lists of things.

Multisets, or bags, are unordered lists that may contain any numbers of items. The following three bags are all equivalent:

[blue red^2] [red blue red] [red red blue]

Natural numbers are multisets in which prime factors are items in the bag, the following two bags are equivalent:

18 [2 3^2]

Items in a bag can be added by multiplication, the two :

18 4
[2 3^2] 2^2
[2^3 3^2]

Items in a bag can be subtracted by division:

18 1/3
[2 3^2] 1/3
[2 3]

Transformations in bags can be represented as fractions in which the contents of the numerator are additions to the bag, and the denumerator, subtractions:

18 5/3
[2 3^2] 5/3
[2 5]

Prime factors can be given names and form the basis of a computation model in which transformations are expressed as symbols in fractions:

• The Carrier Bag Theory of Fiction, Ursula K. Le Guin.

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