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 Th25:
  Mid a,p,a9 & Mid b,p,b9 implies a,b // b9,a9
proof
  assume that
A1: Mid a,p,a9 and
A2: Mid b,p,b9;
  consider d such that
A3: b9,p // a9,d by Def1;
  a,p // p,a9 by A1;
  then
A4: p,a // a9,p by Th7;
  b,p // p,b9 by A2;
  then
A5: p,b // b9,p by Th7;
  a9,d // b9,p by A3,Th3;
  then p,b // a9,d by A5,Def1;
  then
A6: a,b // p,d by A4,Def1;
  b9,a9 // p,d by A3,Def1;
  hence thesis by A6,Def1;
end;
