The reduced Whitehead group is the quotient group
of the Whitehead group by the subgroup generated
by
(Milnor 1966, p. 362). Here, the element
corresponds to the unit
and has order
dividing 2. The general linear group
is the set
of
invertible matrices
with coefficients in an associative ring
with multiplicative
identity, i.e., the set of all units
in an associative unit ring
.