%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/filter { % array proc(bool) -> array
    1 dict begin
    /p exch def
    [ exch
      {
          dup p not
          {
              pop
          } if
      } forall
    ]
    end
} bind def

/test {
    /test.count test.count 1 add def
    {
        /test.pass test.pass 1 add def
    } {
        ( ) print
        test.count (....) cvs print
        (-fail) print
    } ifelse
} bind def

/test.end {
    ( ) print
    test.count 0 gt {
        (Passed ) print
        test.pass (...) cvs print
        (/) print
        test.count (...) cvs print
        ( \() print
        test.pass 100 mul test.count idiv (...) cvs print
        (%\)) print
        (\r\n) print
    } if
} bind def

/test.start {
    print (:) print
    /test.pass 0 def
    /test.count 0 def
} bind def


% end included library code

/beautifularrangement {
    0 dict begin
    /a exch def
    /precalc [
        0 1 a {
            pop
            [
                0 1 a {
                    pop
                    false
                } for
            ]
        } for
    ] def
    1 1 a {
        /i exch def
        i i a {
            /j exch def
            precalc i get j true put
            precalc j get i true put
        } for
    } for
    /ct 0 def
    mark
    [
        1 1 a {
        } for
    ]
    {
        counttomark 0 eq {
            pop exit
        } if
        /trail exch def
        trail length 1 eq {
            /ct ct 1 add def
        } {
            /p a trail length sub 2 add def
            trail {
                /i exch def
                precalc i get p get {
                    trail { i ne } filter
                } if
            } forall
        } ifelse
    } loop
    ct
    end
} bind def

(beautifularrangement) test.start
2 beautifularrangement 2 eq test
1 beautifularrangement 1 eq test
10 beautifularrangement 700 eq test
20 beautifularrangement 1939684 eq test
test.end