let G be IncProjStr ; :: thesis: ( G is configuration iff for p, q being POINT of G
for P, Q being LINE of G st p on P,Q & q on P,Q & not p = q holds
P = Q )

thus ( G is configuration implies for p, q being POINT of G
for P, Q being LINE of G st p on P,Q & q on P,Q & not p = q holds
P = Q ) ; :: thesis: ( ( for p, q being POINT of G
for P, Q being LINE of G st p on P,Q & q on P,Q & not p = q holds
P = Q ) implies G is configuration )

hereby :: thesis: verum
assume A1: for p, q being POINT of G
for P, Q being LINE of G st p on P,Q & q on P,Q & not p = q holds
P = Q ; :: thesis:
now :: thesis: for p, q being POINT of G
for P, Q being LINE of G st p on P & q on P & p on Q & q on Q & not p = q holds
P = Q
let p, q be POINT of G; :: thesis: for P, Q being LINE of G st p on P & q on P & p on Q & q on Q & not p = q holds
P = Q

let P, Q be LINE of G; :: thesis: ( p on P & q on P & p on Q & q on Q & not p = q implies P = Q )
assume ( p on P & q on P & p on Q & q on Q ) ; :: thesis: ( p = q or P = Q )
then ( p on P,Q & q on P,Q ) ;
hence ( p = q or P = Q ) by A1; :: thesis: verum
end;
hence G is configuration ; :: thesis: verum
end;