%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/apush.right { % [a b] c -> [a b c]
    exch
    [ exch aload length 2 add -1 roll ]
} 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

/apop.left { % [a b c] -> [b c] a
    dup 0 get exch
    [ exch aload length -1 roll pop ] exch
} bind def

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


% end included library code

/isas {
    3 dict begin
    /a exch def
    /t a 1 get a 0 get sub def
    true
    2 1 a length 1 sub {
        /i exch def
        a i get a i 1 sub get sub t ne {
            pop
            false
            exit
        } if
    } for
    end
} bind def

/arithmeticsubsequence {
    4 dict begin
    /stack exch [ exch ] def
    0
    {
        stack length 0 eq {
            exit
        } if
        stack apop.left /t exch def /stack exch def
        t isas {
            pop
            t length
            exit
        } {
            0 1 t length 1 sub {
                /i exch def
                stack
                [
                    0 1 t length 1 sub {
                        /ix exch def
                        i ix ne {
                            t ix get
                        } if
                    } for
                ]
                apush.right /stack exch def
            } for
        } ifelse
    } loop
    end
} bind def

(arithmeticsubsequence) test.start
[9 4 7 2 10] arithmeticsubsequence 3 eq test
[3 6 9 12] arithmeticsubsequence 4 eq test
[20 1 15 3 10 5 8] arithmeticsubsequence 4 eq test
test.end