= Dehn presentation
{c}
A finite <group presentation> with cyclically reduced symmetrized <relators> is a <Dehn presentation> if every nonempty freely reduced null word contains a <relator> segment longer than half that <relator>. Replacing the segment by the inverse complementary segment strictly shortens the word. Finiteness of both the alphabet and the <relator> set is part of this definition; merely permitting all null words as an infinite <relator> set would make the shortening property vacuous as a finiteness criterion.
Back to article page
