set(arithmetic).

list(distinct).
  [brother,sister,robinson,mother,0].
end_of_list.

formulas(assumptions).
  brother = robinson + 2.
  sister  = brother  + 4.
  mother  = robinson + 20.
  mother  = brother  + 18.
  mother  = sister   + 14.

  robinson + brother + sister + mother = 39 * 4.  
end_of_list.

