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 Th11:
  not b _|_ a implies x-ProJ(a,b,x)*b _|_ a
proof
  assume
A1: not b _|_ a;
  then ex l being Element of F st x-l*b _|_ a by Def1;
  hence thesis by A1,Def2;
end;
