Sentence:  In the notation of the proof of Theorem 12 , let us take a look at the special case in which the minimal polynomial for T is a product of first degree polynomials , i.e. , the case in which each * * f <WSD>is</WSD> of the form * * f . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)