(   Baker Cooper Fletcher Miller Smith:?people
  & ( constraints
    =
      .   !arg
        : ~(? Baker)
        : ~(Cooper ?)
        : ~(Fletcher ?|? Fletcher)
        : ? Cooper ? Miller ?
        : ~(? Smith Fletcher ?|? Fletcher Smith ?)
        : ~(? Cooper Fletcher ?|? Fletcher Cooper ?)
    )
  & ( solution
    =   floors persons A Z person
      .   !arg:(?floors.?persons)
        & (   !persons:
            & constraints$!floors
            & out$("Inhabitants, from bottom to top:" !floors)
            & ~     { The ~ always fails on evaluation. Here, failure forces Bracmat to backtrack and find all solutions, not just the first one. }
          |   !persons
            :   ?A
                %?`person
                (?Z&solution$(!floors !person.!A !Z))
          )
    )
  & solution$(.!people)
|        { After outputting all solutions, the lhs of the | operator fails. The rhs of the | operator, here an empty string, is the final result. }
);