Integral closure

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In ring theory, the integral closure of a commutative unital ring R in an algebra S over R is the subset of S consisting of all elements of S integral over R: that is, all elements of S satisfying a monic polynomial with coefficients in R. The integral closure is a subring of S.

An example of integral closure is the ring of integers or maximal order in an algebraic number field K, which may be defined as the integral closure of Z in K.

The normalisation of a ring R is the integral closure of R in its field of fractions.