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A normal subgroup (also called an invariant subgroup) is a subgroup H of a group G such that all conjugates of every element in H belong to H. Algebraically, this condition is expressed as $gHg^{-1} = H$ for any element $g$ in G.

Conditions: H is a subgroup of G; The condition must hold for all elements in H; The condition must hold for all elements g in G

A normal subgroup (also called an invariant subgroup) is a subgroup H of a group G such that all conjugates of every element in H belong to H. Algebraically, this condition is expressed as $gHg^{-1} = H$ for any element $g$ in G.

Conditions: H is a subgroup of G; The condition must hold for all elements in H; The condition must hold for all elements g in G