theorem Th61:
  a,a,a,a are_coplanar
  proof
    consider b be POINT of S such that
    between a,a,b and
A1: a <> b by GTARSKI3:36;
    consider c be POINT of S such that
A2: not Collinear a,b,c by A1,GTARSKI3:92;
    consider E be Subset of S such that
    Plane(a,b,c) = E and
A3: E is_plane and
A4: a in E and b in E and c in E by A2,Th49;
    take E;
    thus thesis by A3,A4;
  end;
