for AS being AffinSpace
for a, b, a9, b9 being Element of AS
for M, N, P, Q being Subset of AS st a in M & b in M & a9 in N & b9 in N & a in P & a9 in P & b in Q & b9 in Q & M <> N & M // N & P is being_line & Q is being_line & not P // Q holds
ex q being Element of AS st
( q in P & q in Q )