Sentence:  Then ( a ) * * f ( b ) each * * f <WSD>is</WSD> invariant under T ( c ) if * * f is the operator induced on * * f by T , then the minimal polynomial for * * f is * * f . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)