theorem Th50: :: INCSP_1:50

for S being IncSpace
for A being POINT of S
for P being PLANE of S st A on P holds
ex L, L1, L2 being LINE of S st
( L1 <> L2 & L1 on P & L2 on P & not L on P & A on L & A on L1 & A on L2 )