constructs the HH context

def HH(n):
    """constructs the HH context"""
    if (n<=0):return Context('1')
    else:
        LL1=LL(n-1)
        HH1=HH(n-1)
        r1 = C1(3**(n-1),2**(n-1)) - LL1 - HH1
        r2 = HH1 - HH1 - HH1
        return r1 + r2