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 Th28:
  not b _|_ a & x = 0.S implies PProJ(a,b,x,y) = 0.F
proof
  assume that
A1: not b _|_ a and
A2: x = 0.S;
  for p holds p _|_ a or p _|_ x by A2,Th1,Th2;
  hence thesis by A1,Def3;
end;
