Frieze Groups

cf 
Wilfred Hodges, The geometry of music, pp. 91-111, in:
Fauvel, John, RAymond Flood, and Robin Wilson
Music and Mathematics: From Pythagoras to Fractals
Oxford, 2003

Five motif groups, p. 99

Id, identity
Mv, reflection in a vertical llne
Mh, horizontal
R2, 180 degree rotation

p1: F --- {Id}
ph, C ---  {Id, Mh}
pv: A --- {{Id, Mv}
p2: N --- {Id, R2}
phv: H --- {Id, Mh, Mv, R2}

Seven frieze groups, p. 108

T, translation
G, glide

p1t: FFFF
p1g: FfFf (f = F upside down)
pht: EEEE
pvt: AAAA
pvg: AaAa
p2t: NNNN
phvt: HHHH

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