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Integrally Closed





ORDERED GROUPS


An Ordered Group ''G'' is called integrally closed Iff for all elements ''a'' and ''b'' of ''G'', ''a''n ≤ ''b'' for arbitrary high natural ''n'' implies ''a'' ≤ ''1''.

This property is somewhat stronger than that an ordered group is Archimedean . Though for a Lattice-ordered group to be integrally closed and to be Archimedean is equivalent.
We have the surprising theorem that every integrally closed Directed group is already Abelian .
This have to do with the fact that an Directed group is embeddable into a Complete Lattice-ordered group iff it is integrally closed. Further every archimedean Lattice-ordered group is abelian.


COMMUTATIVE RINGS


A commutative ring R contained in a ring S is said to be integrally closed in S if every element of the Integral Closure of R in S is also in R. Typically if one refers to a domain being integrally closed without reference to an overring, it is meant that the ring is integrally closed in it's field of fractions.

If the ring is not a domain, typically being integrally closed means that every local ring is an integrally closed domain.

Sometimes a domain that is integrally closed is called "normal" if it is integrally closed and being thought of as a variety.
In this respect, the normalization of a Variety (or Scheme ) is simply the Spec of the integral closure of all of the rings.


REFERENCES

  • R. Hartshorne, ''Algebraic Geometry'', Springer-Verlag (1977)

  • M. Atiyah, I. Macdonald ''Introduction to commutative algebra'' Addison-Wesley Publishing Co., Reading, Mass.-London-Don Mills, Ont. 1969

  • H. Matsumura ''Commutative ring theory.'' Translated from the Japanese by M. Reid. Second edition. Cambridge Studies in Advanced Mathematics, 8.