reserve p,p1,p2,q for Point of TOP-REAL 2,
  f,f1,f2,g,g1,g2 for FinSequence of TOP-REAL 2,
  r,s for Real,

  n,m,i,j,k for Nat,
  G for Go-board,
  x for set;
reserve f for non empty FinSequence of TOP-REAL 2;

theorem Th13:
  len GoB(f) = card rng X_axis(f) & width GoB(f) = card rng Y_axis (f)
proof
  set x = X_axis(f), y = Y_axis(f);
  len Incr(x)=card rng x & len Incr(y)=card rng y by SEQ_4:def 21;
  hence thesis by Def1;
end;
