reserve F for Field;
reserve S for OrtSp of F;
reserve a,b,c,d,p,q,r,x,y,z for Element of S;
reserve k,l for Element of F;

theorem Th2:
  a _|_ b implies b _|_ a
proof
  set 0V = 0.S;
  assume a _|_ b;
  then a _|_ (-(-b)) by RLVECT_1:17;
  then
A1: a _|_ 0V-(-b) by RLVECT_1:4;
  0V _|_ -b-a by Th1;
  then -b _|_ a-0V by A1,Def1;
  then -b _|_ a by VECTSP_1:18;
  then (-1_F)*(-b) _|_ a by Def1;
  then -(-b) _|_ a by VECTSP_1:14;
  hence thesis by RLVECT_1:17;
end;
