docs: def wasSolvedBy(self, user):
          """Checks if this exercise has previously been solved by the user.
  
          """
          thisExercise = _Solution.what == self
          byThisUser = _Solution.who == user
          condition = q.AND(thisExercise, byThisUser)
          return self.store.query(_Solution, condition, limit=1).count() == 1