%!PS

/sierp { % level ax ay bx by cx cy
    6 cpy triangle
    sierpr
} bind def

/sierpr {
    12 cpy
    10 -4 2 {
        5 1 roll exch 4 -1 roll
        add 0.5 mul 3 1 roll
        add 0.5 mul 3 -1 roll
        2 roll
    } for       % l a b c bc ac ab
    13 -1 roll dup 0 gt {
        1 sub
        dup 4 cpy 18 -2 roll sierpr
        dup 7 index 7 index 2 cpy 16 -2 roll sierpr
        9 3 roll 1 index 1 index 2 cpy 13 4 roll sierpr
    } { 13 -6 roll 7 { pop } repeat } ifelse
    triangle
} bind def

/cpy { { 5 index } repeat } bind def

/triangle {
    newpath moveto lineto lineto closepath stroke
} bind def

6 50 100 550 100 300 533 sierp
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