reserve AS for AffinSpace;
reserve a,b,c,d,a9,b9,c9,d9,p,q,r,x,y for Element of AS;
reserve A,C,K,M,N,P,Q,X,Y,Z for Subset of AS;

theorem Th37:
  ex X st a in X & b in X & c in X & X is being_plane
proof
  consider A such that
A1: a in A & b in A and
A2: A is being_line by Th11;
  ex X st c in X & A c= X & X is being_plane by A2,Th36;
  hence thesis by A1;
end;
