`define-structure``line-segment``p``q`record`p``l`procedure`q``l`procedure`collinear?``l1``l2`procedure`point-on-line-segment?``r``l`procedure`intersection-point``l1``l2`procedure`cross?``l1``l2`procedure`intersect?``l1``l2`procedure`line-tangent``l`procedure`normal-2d``l`procedure`line-segment-length``l`procedure`read-line-segments-from-file``pathname`procedure`write-line-segments-to-file``line-segments``pathname`procedure