PRIMO(x) := PRIME(x) 

  AGG(x,y) := APPEND(x,[y])

  F(n,r,m) :=   IF( n<=m ,                       ~
                    F( n+1, IF( PRIMO(n) ,     ~
                                AGG(r,n) ,             ~
                                r  )                         ~
                      , m                 ) ,               ~
                 r  )


  PRIMI_FRA(n,m) := F(n, [ ] ,m)