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    Rotation Groups

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    A query, about the orbit PWP{\cal W} in real 3-space of a point PP under an isometry group W{\cal W} generated by edge rotations of a tetrahedron, leads to contrasting notions, W{\cal W} versus S{\cal S}, of "rotation group". The set R ={rA1,rA2}=\{r_{{\sf A}_1},r_{{\sf A}_2}\} of rotations rAir_{{\sf A} _i} about axes Ai{\sf A}_i generates two manifestations of an isometry group on β„œ3\Re^3: (1). In the {\em stationary} group S:=S{\cal S:=S}(R), all axes {\sf B} are fixed under a rotation rAr_{\sf A} about {\sf A}. (2). In the {\em peripatetic} group W:=W{\cal W:=W}(R), each rAr_{\sf A} transforms every rotational axis B=ΜΈA{\sf B\not=A}. {\bf Theorem.} \ If the line A1{\sf A}_1 is skew to A2{\sf A}_2, if each rAir_{{\sf A}_i} is of infinite order, and if Pβˆˆβ„œ3P\in\Re^3, then both of the orbits PSP{\cal S} and PWP{\cal W} are dense in β„œ3\Re^3.Comment: 6 page
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