Symmetry inversion axes
An object has a symmetry inversion axis of order n when the
object remains unchanged after performing the product of a 
rotation around the axis by an inversion with respect to a point located on
the same axis. The used symbol is
. Two objects
related by the inversion axis operation are enantiomorphous; thus if one is
represented by the symbol 
,
the other will be represented by the symbol 
.
In the animation the object is represented by a green sphere, its enantiomorph by a red sphere.
Examples: 
,
, 
,
, 
,
graphical symbol 
.The
rotation of 
is trivial, coincides with the
inversion with respect to the symmetry centre. There are 2 equivalent objects,
one enantiomorphous to the other.
graphical symbol 
if it is normal to the screen, 
if it is parallel to the screen. A symmetrically equivalent point is obtained after
the rotation of 
around the axis followed
by inversion with respect to a point of the axis.
is equivalent to a
mirror perpendicular to the axis ( trace in red ). There are 2 equivalent
objects,
one enantiomorphous to the other.
graphical symbol 
if it is normal to the screen, 
if it is parallel to the screen. A symmetrically equivalent object is obtained after the
rotation of 
followed by inversion with
respect to a point of the axis. It can be seen that
is the
combination of a 3 and
thus:
= 3.
graphical symbol 
if it is normal to the screen, 
if it is parallel to the screen. A symmetrically equivalent object is obtained after the
rotation of 
followed by inversion with
respect to a point of the axis. It can be seen that
is also a
two-fold axis.
graphical symbol 
if it is normal to the screen, 
if it is parallel to the screen. A symmetrically
equivalent object is obtained after the rotation of 
followed by inversion with respect to a point of the axis.
It can be seen that
is the combination of 5 and
, thus:
= 5.
graphical symbol 
if it is normal to the screen, 
if it is parallel to the screen. A symmetrically equivalent object is obtained after the
rotation of 
followed by inversion with
respect to a point of the axis. It can be seen that
is equivalent to the the combination of a threefold axis with a mirror
normal to the axis:
= 3/m.