reserve x,y for set;
reserve X for non empty set;
reserve a,b,c,d for Element of X;
reserve S for OAffinSpace;
reserve a,b,c,d,p,q,r,x,y,z,t,u,w for Element of S;

theorem Th13:
  ex z st Mid x,y,z & y<>z
proof
  consider z such that
A1: x,y // y,z and
  x,y // y,z and
A2: y<>z by ANALOAF:def 5;
  Mid x,y,z by A1;
  hence thesis by A2;
end;
