reserve S for IncStruct;
reserve A,B,C,D for POINT of S;
reserve L for LINE of S;
reserve P for PLANE of S;
reserve F,G for Subset of the Points of S;
reserve a,b,c for Element of {0,1,2,3};
reserve S for IncSpace;
reserve A,B,C,D,E for POINT of S;
reserve K,L,L1,L2 for LINE of S;
reserve P,P1,P2,Q for PLANE of S;
reserve F for Subset of the Points of S;

theorem
  ex B,C,D st not {A,B,C,D} is planar
proof
  set L = the LINE of S;
  consider B such that
A1: A <> B and
  B on L by Lm1;
  ex C,D st not {A,B,C,D} is planar by A1,Th47;
  hence thesis;
end;
