According to "Climbing: Knots" by Nate Fitch and Ron Funderburke, to tie a knot, there must be a tail or bight of rope to ...
The Mule Knot (a.k.a releasable knot) is ideal to lock off the rope on the belay plate. There are many occasions in climbing when, belaying from the harness using a device which does not self-arrest ...