reserve p,q,r for FinSequence;
reserve u,v,x,y,y1,y2,z for object, A,D,X,Y for set;
reserve i,j,k,l,m,n for Nat;

theorem
  rng(p - A) c= rng p
proof
  rng(p - A) = rng p \ A by Th63;
  hence thesis;
end;
