reserve F for Field;
reserve S for SymSp of F;
reserve a,b,c,d,a9,b9,p,q,r,s,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
A1: a _|_ 0V+b by RLVECT_1:4;
  0V _|_ b+a by Th1;
  then b _|_ a+0V by A1,Def1;
  hence thesis by RLVECT_1:4;
end;
