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Minimum and maximum number of lines-[Iran Second Round 1987]

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December 23, 2010
geometry proposedgeometry

Problem Statement

Let L1,L2,L3,L4L_1, L_2, L_3, L_4 be four lines in the space such that no three of them are in the same plane. Let L1,L2L_1, L_2 intersect in AA, L2,L3L_2,L_3 intersect in BB and L3,L4L_3, L_4 intersect in C.C. Find minimum and maximum number of lines in the space that intersect L1,L2,L3L_1, L_2, L_3 and L4.L_4. Justify your answer.
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