Own work -- Converted from the following vector PostScript source code:

%!
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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 648 sqrt sub
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0 y neg 42 270 135 arcn 200 x add 648 sqrt sub x 18 315 45 arc
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
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-100 -100 75 247 225 arcn -17 17 rlineto stroke
100 100 75 67 45 arcn 17 -17 rlineto stroke
0 0 y 42 add 25 36 arc stroke 0 0 y 42 add 205 216 arc stroke
0 0 y 42 add 119 134 arc stroke 0 0 y 42 add 299 314 arc stroke
0 y neg 42 -10 -90 arcn 0 0 y 42 add 270 258 arcn stroke
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117 -83 moveto 83 -117 lineto stroke
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-200 0 moveto 17 17 rmoveto -34 -34 rlineto stroke
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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
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100 x 2 mul add -100 moveto 31 -31 rmoveto 42 -42 rlineto stroke
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y 42 add dup neg 75 add moveto 0 -75 rlineto -75 0 rlineto stroke
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28 setlinewidth .9 .1 .2 setrgbcolor
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100 100 75 68 45 arcn 18 -18 rlineto stroke
0 0 y 42 add 24 37 arc stroke 0 0 y 42 add 204 217 arc stroke
0 0 y 42 add 118 135 arc stroke 0 0 y 42 add 298 315 arc stroke
0 y neg 42 -9 -90 arcn 0 0 y 42 add 270 257 arcn stroke
-118 82 moveto -82 118 lineto stroke
118 -82 moveto 82 -118 lineto stroke
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100 x 2 mul add -100 moveto 18 18 rmoveto -36 -36 rlineto stroke
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100 x 2 mul add -100 moveto 30 -30 rmoveto 44 -44 rlineto stroke
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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

This vector image includes elements that have been taken or adapted from this file:

Celtic-knot-insquare-39crossings.svg .