Ornamental quasi-Celtic knot composed of three repeats of a semi-regular 7-crossings pattern which together fit into a rectangle.  Loosely based on a design in George Bain's Celtic Art: The Methods of Construction, but made from straight lines and 60° and 180° circular arcs.
Self-made image converted from the following vector PostScript source code:

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translate 3{A 550 0 translate}repeat showpage
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AnonMoos