<p>A quasi-Celtic ornamental knot which fills a square.  For much simpler knotwork which fills a square, see <a href="//commons.wikimedia.org/wiki/File:Celtic-knot-insquare-green-transparentbg.svg" title="File:Celtic-knot-insquare-green-transparentbg.svg">File:Celtic-knot-insquare-green-transparentbg.svg</a> .
</p>
For alternative visual realization, see <a href="//commons.wikimedia.org/wiki/File:Celtic-knot-insquare-39crossings_red-on-black.svg" title="File:Celtic-knot-insquare-39crossings red-on-black.svg">File:Celtic-knot-insquare-39crossings red-on-black.svg</a> .
AnonMoos
<p><span class="int-own-work" lang="en">Own work</span> -- Converted from the following vector PostScript source code:
</p>
<pre>%!
306 396 translate .925 dup scale 1 setlinejoin 18 setlinewidth
/x 2812.5 sqrt def/y 3528 sqrt 200 add def .3 .8 .42 setrgbcolor
/A{gsave 42 setlinewidth 0 setgray stroke grestore stroke}def
y 42 add neg dup moveto y 42 add neg x 2 mul y 42 add sub lineto
-100 -100 75 135 225 arcn -200 x sub x neg lineto 0 y 42 -45 90 arc
0 0 y 42 add 90 270 arc 0 y neg 42 -90 45 arc -200 x sub x lineto
-100 100 75 135 225 arcn y 42 add neg y 42 add x 2 mul sub lineto
y 42 add neg dup neg lineto A y 42 add dup neg moveto
y 42 add x 2 mul y 42 add sub lineto 100 -100 75 45 315 arc
200 x add x neg lineto 0 y 42 225 90 arcn 0 0 y 42 add 90 -90 arcn
0 y neg 42 270 135 arcn 200 x add x lineto 100 100 75 45 315 arc
y 42 add y 42 add x 2 mul sub lineto y 42 add dup lineto A
y 42 add neg dup neg moveto -175 y 42 add lineto
-100 100 x 2 mul add 75 180 225 arc
100 100 x 2 mul add neg 75 45 0 arcn 175 y 42 add neg lineto
y 42 add dup neg lineto A y 42 add neg dup moveto
-175 y 42 add neg lineto -100 100 x 2 mul add neg 75 180 135 arcn
100 100 x 2 mul add 75 315 0 arc 175 y 42 add lineto
y 42 add dup lineto A 0 setlinejoin 42 setlinewidth 0 setgray
-100 -100 75 25 65 arc stroke 100 100 75 205 245 arc stroke
-100 100 75 25 65 arc stroke 100 -100 75 205 245 arc stroke
-100 100 75 245 225 arcn -16 16 rlineto stroke
100 -100 75 65 45 arcn 16 -16 rlineto stroke
-100 -100 75 245 225 arcn -16 16 rlineto stroke
100 100 75 65 45 arcn 16 -16 rlineto stroke
0 0 y 42 add 25 35 arc stroke 0 0 y 42 add 205 215 arc stroke
0 0 y 42 add 119 134 arc stroke 0 0 y 42 add 299 314 arc stroke
0 y neg 42 -14 -90 arcn 0 0 y 42 add 270 258 arcn stroke
-116 84 moveto -84 116 lineto stroke
116 -84 moveto 84 -116 lineto stroke
0 200 moveto 16 16 rmoveto -32 -32 rlineto stroke
200 0 moveto 16 16 rmoveto -32 -32 rlineto stroke
-200 0 moveto 16 16 rmoveto -32 -32 rlineto stroke
100 x 2 mul add 100 moveto 16 16 rmoveto -32 -32 rlineto stroke
100 x 2 mul add neg 100 moveto 16 16 rmoveto -32 -32 rlineto stroke
100 x 2 mul add -100 moveto 16 16 rmoveto -32 -32 rlineto stroke
100 x 2 mul add neg -100 moveto 16 16 rmoveto -32 -32 rlineto stroke
100 x sub 100 x add moveto -16 16 rmoveto 32 -32 rlineto stroke
100 x add 100 x sub moveto -16 16 rmoveto 32 -32 rlineto stroke
-100 x sub -100 x add moveto -16 16 rmoveto 32 -32 rlineto stroke
-100 x add -100 x sub moveto -16 16 rmoveto 32 -32 rlineto stroke
100 x 2 mul add neg 100 moveto -34 34 rmoveto -37 37 rlineto stroke
100 x 2 mul add -100 moveto 34 -34 rmoveto 37 -37 rlineto stroke
y 42 add dup 75 sub moveto 0 75 rlineto -75 0 rlineto stroke
y 42 add neg dup 75 add moveto 0 -75 rlineto 75 0 rlineto stroke
y 42 add dup neg 75 add moveto 0 -75 rlineto -75 0 rlineto stroke
y 42 add neg dup neg 75 sub moveto 0 75 rlineto 75 0 rlineto stroke
.3 .8 .42 setrgbcolor 18 setlinewidth
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-100 100 75 24 66 arc stroke 100 -100 75 204 246 arc stroke
-100 100 75 246 225 arcn -17 17 rlineto stroke
100 -100 75 66 45 arcn 17 -17 rlineto stroke
-100 -100 75 246 225 arcn -17 17 rlineto stroke
100 100 75 66 45 arcn 17 -17 rlineto stroke
0 0 y 42 add 24 36 arc stroke 0 0 y 42 add 204 216 arc stroke
0 0 y 42 add 118 135 arc stroke 0 0 y 42 add 298 315 arc stroke
0 y neg 42 -13 -90 arcn 0 0 y 42 add 270 257 arcn stroke
-117 83 moveto -83 117 lineto stroke
117 -83 moveto 83 -117 lineto stroke
0 200 moveto 17 17 rmoveto -34 -34 rlineto stroke
200 0 moveto 17 17 rmoveto -34 -34 rlineto stroke
-200 0 moveto 17 17 rmoveto -34 -34 rlineto stroke
100 x 2 mul add 100 moveto 17 17 rmoveto -34 -34 rlineto stroke
100 x 2 mul add neg 100 moveto 17 17 rmoveto -34 -34 rlineto stroke
100 x 2 mul add -100 moveto 17 17 rmoveto -34 -34 rlineto stroke
100 x 2 mul add neg -100 moveto 17 17 rmoveto -34 -34 rlineto stroke
100 x sub 100 x add moveto -17 17 rmoveto 34 -34 rlineto stroke
100 x add 100 x sub moveto -17 17 rmoveto 34 -34 rlineto stroke
-100 x sub -100 x add moveto -17 17 rmoveto 34 -34 rlineto stroke
-100 x add -100 x sub moveto -17 17 rmoveto 34 -34 rlineto stroke
100 x 2 mul add neg 100 moveto -33 33 rmoveto -39 39 rlineto stroke
100 x 2 mul add -100 moveto 33 -33 rmoveto 39 -39 rlineto stroke
y 42 add dup 76 sub moveto 0 76 rlineto -76 0 rlineto stroke
y 42 add neg dup 76 add moveto 0 -76 rlineto 76 0 rlineto stroke
y 42 add dup neg 76 add moveto 0 -76 rlineto -76 0 rlineto stroke
y 42 add neg dup neg 76 sub moveto 0 76 rlineto 76 0 rlineto stroke
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%EOF</pre>