Sentence:  Now the only way in which all curves of the image family of * * f can pass through a fixed point is to have a generator of * * f which <WSD>is</WSD> not a secant but a tangent of \ g , for then any point on such a generator will be transformed into the point of tangency . 
Meaning of the word marked with <WSD> tags:  be identical to; be someone or something