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) = rng p implies A misses rng p
proof
  assume rng(p - A) = rng p;
  then rng p \ A = rng p by Th63;
  hence thesis by XBOOLE_1:83;
end;
