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Section 18.1 Pre-read

Suppose G is a group acting on a set X. Recall that the Stabilizer of set element \(x\) is the subgroup of those group elements g so that g(x)=x. There is a related dual concept to the concept of stabilizer.

Definition 18.1.1. Fixed set of a group element g.

Write Xg or FixX(g) to mean the collection of those set elements x so that g(x)=x.

Warning 18.1.2. Keep it straight!

A stabilizer is a subgroup of group elements from G that fix a single set element x in common, while a fixed set is a collection of set elements from X that are fixed in common by a single group element g.