Dehn presentation of a knot group
= Dehn presentation of a knot group
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{wiki=Dehn_presentation}
Give every region of a <knot diagram> a generator and set the generator of the unbounded region to the identity. At a crossing, reading the four incident regions cyclically gives a relation $a b^{-1}c d^{-1}=1$, with the cyclic order reversed if the opposite convention is chosen. These relations form the Dehn presentation of the knot group.