code: def BB(n):
      
      if (n<=1):return Context('0\n1')
      else:
          BB1=BB(n-1)
          AA1=AA(n-1)
          r1 = C1((n-1)*2**(n-2),2**(n-1)) - AA1 - BB1
          r2 = BB1 - C1(2**(n-1),2**(n-1)) - BB1;
          return r1 + r2
docs: constructs the BB context