The historically attested instances of the symbol appear in two traditional, topologically distinct, forms. The symbol appears in unicursal form, topologically a trefoil knot also seen in the triquetra. This unicursal form is found, for example, on the Tängelgårda stone. The symbol also appears in tricursal form, consisting of three linked triangles, topologically equivalent to the Borromean rings. This tricursal form can be seen on one of the Stora Hammars stones, as well as upon the Nene River Ring, and on the Oseberg ship bed post. Although other forms are topologically possible, these are the only attested forms found so far.