Definition of "subalgebra" []

• A closed subset of an algebra. (noun)

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• "Then a state is operationally separated with respect to T if T's application does not change the result of applying the state to any element of the other subalgebra: it is operationally separable with respect to T if it is operationally separated, either with respect to T, or with respect to some other operation T* that coincides with the action of T on the other subalgebra."
• "As I pointed out, the subalgebra generated by L_m with m 0 contains no reference to the conformal anomaly."
• "Hence this subalgebra admits a nilpotent BRST operator, and can be viewed as a gauge symmetry."