reserve AS for AffinSpace;
reserve a,a9,b,b9,c,d,o,p,q,r,s,x,y,z,t,u,w for Element of AS;
reserve A,C,D,K for Subset of AS;

theorem
  a<>b & A=Line(a,b) iff A is being_line & a in A & b in A & a<>b by Lm6
