?? hmm ... in the visualization talk i had a bit of trouble with "non-individuality of the poles of the axis/skewer" in the gimbal/axis picture of the real algebraic b2 building ... ?? maybe the best approach is to emphasize points as configurations of a mechanical system in contrast to lines as mere subspaces of that configuration space ... thus the gimbal is officially part of the mechanical system whereas the skewer isn't; it's just there (?? "auxiliary" ?? ...) to remind you where the spin axis is .... so that "explains" why pulling the skewer out and putting it back in backwards doesn't change the line .... ??? ....