Free ideal ring

Free ideal ring

In mathematics, especially in the field of ring theory, a (left) free ideal ring, or fir, is a ring in which all left ideals are free of unique rank. A ring such that all left ideals with at most "n" generators is free of unique rank is called an n-fir. A semi-fir is a ring in which all finitely generated left ideals are free of unique rank.

A commutative ring is a fir if and only if it is a principal ideal domain (a PID). Thus, the concept fir is a kind of generalisation of the concept PID to not necessarily commutative rings, and the firs partially have similar properties as PIDs; e.g., they have global homological dimension (at most) one. However, a fir is not necessarily Noetherian.

Another important and motivating example of a free ideal ring are the free associative (unital) "k"-algebras for division rings "k", also called non-commutative polynomial rings harv|Cohn|2000|loc=§5.4. Every free ideal ring has the invariant basis number property.

References

* | year=2006 | volume=3
*Citation | last1=Cohn | first1=P. M. | title=Free rings and their relations | publisher=Academic Press | location=Boston, MA | edition=2nd | series=London Mathematical Society Monographs | isbn=978-0-12-179152-0 | id=MathSciNet | id = 800091 | year=1985 | volume=19
* | year=2000
*springer|id=F/f041580


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