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 Th40:
  for A being being_line Subset of AS holds A // A
proof
  let A be being_line Subset of AS;
  consider a,b such that
A1: a<>b and
A2: A=Line(a,b) by Def3;
  a,b // a,b by Th1;
  hence thesis by A1,A2,Th36;
end;
