The group torsion 
of a group 
is the set of elements 
in 
such that 
for some positive
integer 
,
where 
is the identity element of the group 
.
In the case that 
is Abelian, 
is a subgroup and is called
the torsion subgroup of 
. If 
consists only of the identity
element, the group 
is called torsion-free.
