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monic polynomial

Definition

Given a unital ring $k$, a monic polynomial over $k$ is a polynomial with coefficients in $k$, whose highest order coefficient is $1$.

A root of a monic polynomial over $k$ is by definition an algebraic integer over $k$.

Here algebraic integer usually means algebraic integer over $\mathbf{Z}$. All algebraic integers form a field called the integral closure of $\mathbf{Z}$ in $\mathbf{C}$.

On the other hand, for a number field $K$, an integer in $K$ is an algebraic integer over $\mathbf{Z}$ which is in $K$; all integers in $K$ form a ring of integers $\mathcal{O}_K$ of the number field $K$.

References

• Wikipedia, Algebraic number