constructs the LL context

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