reserve AFV for WeakAffVect;
reserve a,b,c,d,e,f,a9,b9,c9,d9,f9,p,q,r,o,x99 for Element of AFV;

theorem Th22:
  Mid a,b,c & Mid a,b,c9 implies c = c9
proof
  assume that
A1: Mid a,b,c and
A2: Mid a,b,c9;
  a,b // b,c9 by A2;
  then
A3: b,c9 // a,b by Th3;
  a,b // b,c by A1;
  then b,c // a,b by Th3;
  then b,c // b,c9 by A3,Def1;
  hence thesis by Th4;
end;
