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*Definition:*
A set `S` is *finite* if it is empty or there is a bijection to
**N**_{n} for some `n` > 0. We then call 0
resp. `n` the *size* or
*cardinality* of `S`:

A set is

Sis finite : <=>S=0\/( existsninN_{>0},f:f:N_{n}->^{bijective}S);| S| :=ifS=0then0else( suchninN_{>0}:existsf:f:N_{n}->^{bijective}S).

Sis infinite : <=> ~Sis finite.

Author: Wolfgang Schreiner

Last Modification: December 7, 1999