theorem Th3: :: PROJRED2:3

for IPP being 2-dimensional Desarguesian IncProjSp
for o, y being POINT of IPP
for A, B being LINE of IPP st not o on A & not o on B & y on B holds
ex x being POINT of IPP st
( x on A & (IncProj (A,o,B)) . x = y )