"Please define what you mean as a league, my personal definition is the distance traveled best defined as the integral of..." She proceeded to list off a long formula that would end up resulting in her being about 500 feet away from where she currently is. "I also want your assurance that neither you, nor anyone you have associated with, will impede my movement. Does that work for you?" Hopefully the devil would not check the math and it would let her get away. Because there is no way she could move using the actual definition of a league.