let AS be AffinSpace; for q being Element of
for K, M being Subset of st q in K & q in M & K is being_line & M is being_line holds
( K,M,M is_coplanar & M,K,M is_coplanar & M,M,K is_coplanar )
let q be Element of ; for K, M being Subset of st q in K & q in M & K is being_line & M is being_line holds
( K,M,M is_coplanar & M,K,M is_coplanar & M,M,K is_coplanar )
let K, M be Subset of ; ( q in K & q in M & K is being_line & M is being_line implies ( K,M,M is_coplanar & M,K,M is_coplanar & M,M,K is_coplanar ) )
assume
( q in K & q in M & K is being_line & M is being_line )
; ( K,M,M is_coplanar & M,K,M is_coplanar & M,M,K is_coplanar )
then
ex X being Subset of st
( K c= X & M c= X & X is being_plane )
by Th38;
hence
( K,M,M is_coplanar & M,K,M is_coplanar & M,M,K is_coplanar )
by Def5; verum