For a nilpotent ideal , its nilpotence index of an ideal is the least positive integer for which . In , with an irreducible polynomial, the unique maximal ideal has index . In a discrete valuation ring with , the maximal ideal of its reduction modulo has the same index. Comparing these indices under a quotient ring isomorphism recovers the ramification exponent in the Kummer-Dedekind theorem.
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In abstract algebra, specifically in the study of rings, a **nilpotent ideal** is an ideal such that there exists some positive integer \( n \) for which the \( n \)-th power of the ideal is equal to the zero ideal.