reserve F for Field;
reserve a,b,c,d,p,q,r for Element of MPS(F);
reserve e,f,g,h,i,j,k,l,m,n,o,w for Element of [:the carrier of F,the carrier
  of F,the carrier of F:];
reserve K,L,M,N,R,S for Element of F;
reserve FdSp for FanodesSp;
reserve a,b,c,d,p,q,r,s,o,x,y for Element of FdSp;

theorem
  a,b congr a,b
proof
  now
    assume a<>b;
    then consider p,q such that
A1: parallelogram a,b,p,q by Th43;
    parallelogram p,q,a,b by A1,Th33;
    hence thesis;
  end;
  hence thesis;
end;
