Washington’s law, called I-502, takes effect on Dec. 6, which also leaves a year of limbo during which the state licensing system will not yet exist, but legalized possession will. And there are thorny mechanical questions that must be resolved during that time, like how to balance the state’s mandate of “adequate access” to licensed marijuana with its prohibitions on cannabis businesses within 1,000 feet of a school, park, playground or child care center.