divisor theory and exponent valuations
A divisor theory of an integral domain
determines via its prime divisors
a certain set of exponent valuations on the quotient field of . Assume to be known this set of exponents (http://planetmath.org/ExponentValuation2) corresponding the prime divisors . There is a bijective
correspondence between the elements of and of the set of all prime divisors. The set of the prime divisors determines completely the of the free monoid of all divisors
in question. The homomorphism
is then defined by the condition
(1) |
since for any element of there exists only a finite number of exponents which do not vanish on (corresponding the different prime divisor factors (http://planetmath.org/DivisibilityInRings) of the principal divisor ).
One can take the concept of exponent as foundation for divisor theory:
Theorem. Let be an integral domain with quotient field and a given set of exponents (http://planetmath.org/ExponentValuation2) of . The exponents in determine, as in (1), a divisor theory of iff the following three conditions are in :
- •
For every there is at most a finite number of exponents such that .
- •
An element belongs to if and only if for each .
- •
For any finite set
of distinct exponents in and for the arbitrary set of non-negative integers, there exists an element of such that
For the proof of the theorem, we mention only how to construct the divisors when we have the exponent set fulfilling the three conditions of the theorem. We choose a commutative monoid that allows unique prime factorisation and that may be mapped bijectively onto . The exponent in which corresponds to arbitrary prime element
is denoted by . Then we obtain the homomorphism
which can be seen to satisfy all required properties for a divisor theory .
References
- 1 S. Borewicz & I. Safarevic: Zahlentheorie. Birkhäuser Verlag. Basel und Stuttgart (1966).