( ( Amb
  =   first last list words word solution
    .   !arg:(?first.?list)
      & ( !list:
        |   !list:(.?words) ?list
          &   !words
            :   ?
                %( @(?word:!first ? @?last)
                 & Amb$(!last.!list):?solution
                 & !word !solution:?solution
                 )
                ?
          & !solution
        )
  )
&   Amb
  $ (
    .   (.the that a)
        (.frog elephant thing)
        (.walked treaded grows)
        (.slowly quickly)
    )
)