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We observe first that no line, l, can meet its image except at one of its intersections with Q.

For if it did, the plane of L and l' would contain two generators of Af, which is impossible.

Moreover, from the definitive transformation of intercepts on the generators of Af, it is clear that the only points of Q at which a line can meet its image are the points of Aj.

Hence the totality of singular lines is the T order complex of lines which meet Aj.