Dehn invariant
... that it is unknown if the Dehn invariant of a flexible polyhedron stays invariant as it flexes?
... that it is unknown if the <b id="mwBQQ"><a href="./Dehn_invariant" id="mwBQU" rel="mw:WikiLink" title="Dehn invariant">Dehn invariant</a></b> of a <a href="./Flexible_polyhedron" id="mwBQY" rel="mw:WikiLink" title="Flexible polyhedron">flexible polyhedron</a> stays invariant as it flexes?