Right-handed Dehn twist
= Right-handed Dehn twist
= Positive Dehn twist
{synonym}
In orientation-preserving annular coordinates $(\theta,r)$ with orientation $d\theta\wedge dr$, the twist is $(\theta,r)\mapsto(\theta+2\pi f(r),r)$, where $f$ increases from zero to one. The map is the identity outside this <annulus> and near its boundary. The orientation of the ambient <topological surface>, rather than the orientation assigned to the curve, fixes the handedness.