%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/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

/combinations {
    4 dict begin
    /k exch def
    /arr exch def
    /c [
        0 1 k 1 sub { } for
        arr length
        0
    ] def
    [
        {
            [
                k 1 sub -1 0 {
                    c exch get arr exch get
                } for
            ]
            /j 0 def
            {
                c j get 1 add c j 1 add get ne {
                    exit
                } if
                c j j put
                /j j 1 add def
            } loop
            j k ge {
                exit
            } if
            c j c j get 1 add put
        } loop
    ]
    end
} bind def

/filter { % array proc(bool) -> array
    1 dict begin
    /p exch def
    [ exch
      {
          dup p not
          {
              pop
          } if
      } forall
    ]
    end
} bind def

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


% end included library code

/reversepairs {
    2 combinations
    { aload pop exch 2 mul gt } filter
    length
} bind def

(reversepairs) test.start
[1 3 2 3 1] reversepairs 2 eq test
[2 4 3 5 1] reversepairs 3 eq test
test.end