anchor.diff:  . Smart-ass extra credit: Why does the problem description stipulate that some cleaners don't work full-time?
   What would happen if they all work full-time?
   
  -Presume there's `Location` class with a functioning `long getDistance(Location)` method.
  +Presume there is a `Location` class with a functioning `long getDistance(Location)` method.
   
   ==== Success criteria
   
  
positive.code: * Why is `House` is the planning entity and not `Cleaner`?
  ** 1 cleaner handles multiple houses, but 1 house has only 1 cleaner, so `House` has a _manyToOne_ relationship to `Cleaner`.
  ** Furthermore, the number of `House` instances is stable during planning.
  * What about the traveling distance constraint? Isn't this like Vehicle Routing?
  Isn't the planning variable _chained_?
  ** No. The cleaners go home after every house.
  ** So it doesn't matter what house they cleaned the day before, because they always have to go home first.
  ** So it's not like TSP/VRP. So there's no need for the complexity of chained planning variables.
  ** Furthermore, because the DayOfWeek is fixed, introducing chained variables would require additional constraint rules.
  
  
negative.code: 
  ==== Problem description
  
  A cleaning company cleans houses. It needs to match cleaners and houses in a week.
  
  * Each cleaner cleans exactly 1 house per day. He/she cleans it entirely during that day, alone.
  * Each house needs to be cleaned once, at a specified day of the week (determined by the house owner).
  * A cleaner works from Monday to Friday. some cleaners work only 3 days in a week, but the company can chose when.
  * A cleaner travels from his/her home to one house in the morning and travels back in the evening.
  
  Plan a schedule of the cleaning company for an entire week. Minimize the overall travelling distance of the cleaners.
  
  ==== Assignment
  
  