Sentence:  Then in 2 we show that any line involution with the properties that ( a ) It has no complex of invariant lines , and ( b ) Its singular lines <WSD>form</WSD> a complex consisting exclusively of the lines which meet a twisted curve , is necessarily of the type discussed in 1 . 
Meaning of the word marked with <WSD> tags:  to compose or represent:"This wall forms the background of the stage setting"