theorem Th62:
  a,a,a,b are_coplanar
  proof
    per cases;
    suppose a = b;
      hence thesis by Th61;
    end;
    suppose a <> b;
      then consider a9 be POINT of S such that
A1:   not Collinear a,b,a9 by GTARSKI3:92;
      ex E be Subset of S st Plane(a,b,a9) = E & E is_plane & a in E &
        b in E & a9 in E by A1,Th49;
      hence thesis;
    end;
  end;
