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
  K,M,N is_coplanar implies K,N,M is_coplanar & M,K,N is_coplanar
  & M,N,K is_coplanar & N,K,M is_coplanar & N,M,K is_coplanar;
