= Holonomy groups of closed orientable flat three-manifolds
{title2=$1,\ C_2,\ C_3,\ C_4,\ C_6,\ C_2\times C_2$}
These are precisely the faithful linear holonomy groups of closed orientable Euclidean three-manifolds. Cyclic cases arise from planar lattice rotations combined with axial screw translations. The noncyclic case is generated by two perpendicular half-turn screws. The list refers to the maximal translation lattice, not to arbitrary finite quotients of a <fundamental group>.
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