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 Th6:
  a _|_ b implies -a _|_ b
proof
  assume a _|_ b;
  then (-1_F)*a _|_ b by Def1;
  hence thesis by VECTSP_1:14;
end;
