komu

> {-# OPTIONS -Wall -XMultiParamTypeClasses -XFunctionalDependencies -XTypeSynonymInstances #-}
> module Main where

8 people are standing on a west bank of a river and must cross to the
other side using a boat. However,

  - the boat carries at most 2 people at a time,
  - the father can't be left with the girls without the mother,
  - the mother can't be left with the boys without the father,
  - the prisoner can't be left with any family members without the police,