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Dan Hoey's Taxonomy of Symmetry Groups and Shoenflies Symbols
Submitted by Jerry Bryan on Thu, 02/22/2007 - 23:40.
I have received permission to post Dan Hoey's taxonomy of symmetry groups of Rubik's Cube. Also, I will relate Dan's taxonomy to Shoenflies symbols as implemented in Herbert Kociemba's Cube Explorer. (Go to http://kociemba.org/cube.htm and then click on Symmetric Patterns.) To that end, some preparatory comments are in order. In order to define any terminology for the symmetry groups of Rubik's Cube, it's necessary first to define some terminology for the symmetries of the cube. To the best of my knowledge, no standard terminology has been adopted by the Rubik's cube community for the symmetries of the cube. The terminology I'm going to use is very similar to some terminology I have seen before, but I can't remember the reference. It may have been Christoph Bandelow's book, Inside Rubik's Cube and Beyond. In any case, if I can find the reference I want to give proper credit. Cube symmetries are either rotations and reflections. For rotations, the terminology I'm going to use will be based on the axis of rotation for the various symmetries. A cube contains three kinds of axes of symmetry. It will prove convenient to describe the three kinds of axes in terms of Rubik's Cube faces and cubies.
We can now define the 24 cube rotations in terms of those three kinds of axes.
For the reflections, I'm going to arrive at Dan Hoey's taxonomy simply by multiplying all the rotations by a reflection. If C is the set of 24 rotations and if f is any reflection, then it is the case that fC=Cf. The choice of f is arbitrary. However, it is in general not the case that fc=cf for every element c of C. It is not necessary for fc=cf for all c in C in order that fC=Cf. However, it is convenient to choose f such that fc=cf for all c in C. There is only one such reflection that commutes with all the rotations, namely the central inversion that we will denote as v. Hence, we have vC=Cv, and we also have cv=vc for all c in C. In Dan Hoey's taxonomy, the convention of generating the reflections as vC or Cv yields the following. l1=v(i1) r1=v(q1) j1=v(k1) h1=v(g1) e1=v(d1) r2=v(q2) j2=v(k2) h2=v(g2) e2=v(d2) r3=v(q3) j3=v(k3) h3=v(g3) e3=v(d3) r4=v(q4) h4=v(g4) e4=v(d4) r5=v(q5) h5=v(g5) e5=v(d5) r6=v(q6) h6=v(g6) e6=v(d6) h7=v(g7) h8=v(g8) The following table lists the 98 subgroups of M, and also the corresponding 33 symmetry classes. The subgroups are arranged by symmetry class, and the symmetry class name is given both in terms of Dan Hoey's taxonomy, and in terms of Shoenflies symbols. The subgroups within any particular symmetry class are respectively conjugate subgroups of each other. I1 = {i1} I = {I1} Shoenflies symbol = C1 HV1 = {i1,l1} HV = {HV1} Shoenflies symbol = Ci AV1 = {i1,e1} AV2 = {i1,e2} AV3 = {i1,e3} AV4 = {i1,e4} AV5 = {i1,e5} AV6 = {i1,e6} AV = {AV1,AV2,AV3,AV4,AV5,AV6} Shoenflies symbol = Cs(b) CV1 = {i1,d1} CV2 = {i1,d2} CV3 = {i1,d3} CV4 = {i1,d4} CV5 = {i1,d5} CV6 = {i1,d6} CV = {CV1,CV2,CV3,CV4,CV5,CV6} Shoenflies symbol = C2(b) HW1 = {i1,j1} HW2 = {i1,j2} HW3 = {i1,j3} HW = {HW1,HW2,HW3} Shoenflies symbol = Cs(a) ES1 = {i1,k1} ES2 = {i1,k2} ES3 = {i1,k3} ES={ES1,ES2,ES3} Shoenflies symbol = C2(a) ET1 = {i1,g1,g2} ET2 = {i1,g3,g4} ET3 = {i1,g5,g6} ET4 = {i1,g7,g8} ET= = {ET1,ET2,ET3,ET4} Shoenflies symbol = C3 V1 = {i1,l1,e1,d1} V2 = {i1,l1,e2,d2} V3 = {i1,l1,e3,d3} V4 = {i1,l1,e4,d4} V5 = {i1,l1,e5,d5} V6 = {i1,l1,e6,d6} V = {V1,V2,V3,V4,V5,V6} Shoenflies symbol = C2h(b) W1 = {i1,j1,e1,d2} W2 = {i1,j1,e2,d1} W3 = {i1,j2,e3,d4} W4 = {i1,j2,e4,d3} W5 = {i1,j3,e5,d6} W6 = {i1,j3,e6,d5} W = {W1,W2,W3,W4,W5,W6} Shoenflies symbol = C2v(b) HS1 = {i1,l1,k1,j1} HS2 = {i1,l1,k2,j2} HS3 = {i1,l1,k3,j3} HS = {HS1,HS2,HS3} Shoenflies symbol = C2h(a) AS1 = {i1,k1,e1,e2} AS2 = {i1,k2,e3,e4} AS3 = {i1,k3,e5,e6} AS = {AS1,AS2,AS3} Shoenflies symbol = C2h(a) CR1 = {i1,k1,q1,q2} CR2 = {i1,k2,q3,q4} CR3 = {i1,k3,q5,q6} CR = {CR1,CR2,CR3} Shoenflies symbol = C4 HQ1 = {i1,k1,j2,j3} HQ2 = {i1,k2,j1,j3} HQ3 = {i1,k3,j1,j2} HQ = {HQ1,HQ2,HQ3} Shoenflies symbol = C2v(a2) AP1 = {i1,k1,r1,r2} AP2 = {i1,k2,r3,r4} AP3 = {i1,k3,r5,r6} AP = {AP1,AP2,AP3} Shoenflies symbol = S4 CS1 = {i1,k1,d1,d2} CS2 = {i1,k2,d3,d4} CS3 = {i1,k3,d5,d6} CS = {CS1,CS2,CS3} Shoenflies symbol = D2 (edge) EX1 = {i1,k1,k2,k3} EX = {EX1} Shoenflies symbol = D2 (face) HT1 = {i1,l1,g1,g2,h1,h2} HT2 = {i1,l1,g3,g4,h3,h4} HT3 = {i1,l1,g5,g6,h5,h6} HT4 = {i1,l1,g7,g8,h7,h8} HT = {HT1,HT2,HT3,HT4} Shoenflies symbol = S6 AT1 = {i1,e1,e4,e5,g1,g2} AT2 = {i1,e2,e3,e5,g3,g4} AT3 = {i1,e1,e3,e6,g5,g6} AT4 = {i1,e2,e4,e6,g7,g8} AT = {AT1,AT2,AT3,AT4} Shoenflies symbol = C3v CT1 = {i1,d1,d4,d5,g1,g2} CT2 = {i1,d2,d3,d5,g3,g4} CT3 = {i1,d1,d3,d6,g5,g6} CT4 = {i1,d2,d4,d6,g7,g8} CT = {CT1,CT2,CT3,CT4} Shoenflies symbol = D3 S1 = {i1,l1,k1,j1,e1,e2,d1,d2} S2 = {i1,l1,k2,j2,e3,e4,d3,d4} S3 = {i1,l1,k3,j3,e5,e6,d5,d6} S = {S1,S2,S3} Shoenflies symbol = D2h (edge) Q1 = {i1,k1,j2,j3,e1,e2,q1,q2} Q2 = {i1,k2,j1,j3,e3,e4,q3,q4} Q3 = {i1,k3,j1,j2,e5,e6,q5,q6} Q = {Q1,Q2,Q3} Shoenflies symbol = C4v R1 = {i1,l1,k1,j1,q1,q2,r1,r2} R2 = {i1,l1,k2,j2,q3,q4,r3,r4} R3 = {i1,l1,k3,j3,q5,q6,r5,r6} R = {R1,R2,R3} Shoenflies Symbol = C4h P1 = {i1,k1,j2,j3,d1,d2,r1,r2} P2 = {i1,k2,j1,j3,d3,d4,r3,r4} P3 = {i1,k3,j1,j2,d5,d6,r5,r6} P = {P1,P2,P3} Shoenflies Symbol = D2d (edge) HX1 = {i1,l1,k1,k2,k3,j1,j2,j3} HX = {HX1} Shoenflies Symbol = D2h (face) AX1 = {i1,k1,k2,k3,e1,e2,r1,r2} AX2 = {i1,k1,k2,k3,e3,e4,r3,r4} AX3 = {i1,k1,k2,k3,e5,e6,r5,r6} AX = {AX1,AX2,AX3} Shoenflies Symbol = D2d (face) CX1 = {i1,k1,k2,k3,d1,d2,q1,q2} CX2 = {i1,k1,k2,k3,d3,d4,q3,q4} CX3 = {i1,k1,k2,k3,d5,d6,q5,q6} CX = {CX1,CX2,CX3} Shoenflies Symbol = D4 T1 = {i1,l1,e1,e4,e5,d1,d4,d5,g1,g2,h1,h2} T2 = {i1,l1,e2,e3,e5,d2,d3,d5,g3,g4,h3,h4} T3 = {i1,l1,e1,e3,e6,d1,d3,d6,g5,g6,h5,h6} T4 = {i1,l1,e2,e4,e6,d2,d4,d6,g7,g8,h7,h8} T = {T1,T2,T3,T4} Shoenflies Symbol = D3d E1 = {i1,k1,k2,k3,g1,g2,g3,g4,g5,g6,g7,g8} E = {E1} Shoenflies Symbol = T X1 = {i1,l1,k1,k2,k3,j1,j2,j3,e1,e2,d1,d2,q1,q2,r1,r2} X2 = {i1,l1,k1,k2,k3,j1,j2,j3,e3,e4,d3,d4,q3,q4,r3,r4} X3 = {i1,l1,k1,k2,k3,j1,j2,j3,e5,e6,d5,d6,q5,q6,r5,r6} X = {X1,X2,X3} Shoenflies Symbol = D4h H1 = {i1,l1,k1,k2,k3,j1,j2,j3,g1,g2,g3,g4,g5,g6,g7,g8, h1,h2,h3,h4,h5,h6,h7,h8} H = {H1} Shoenflies Symbol = Th A1 = {i1,k1,k2,k3,e1,e2,e3,e4,e5,e6,r1,r2,r3,r4,r5,r6, g1,g2,g3,g4,g5,g6,g7,g8} A = {A1} Shoenflies Symbol = Td C1 = {i1,k1,k2,k3,d1,d2,d3,d4,d5,d6,q1,q2,q3,q4,q5,q6, g1,g2,g3,g4,g5,g6,g7,g8} C = {C1} Shoenflies Symbol = O M1 = {i1,l1,k1,k2,k3,j1,j2,j3,e1,e2,e3,e4,e5,e6, d1,d2,d3,d4,d5,d6,q1,q2,q3,q4,q5,q6, r1,r2,r3,r4,r5,r6,g1,g2,g3,g4,g5,g6,g7,g8, h1,h2,h3,h4,h5,h6,h7,h8} M = {M1} Shoenflies Symbol = Oh |
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