In: Advanced Math
Abstract Algebra
Let n ≥ 2. Show that Sn is generated by each of the following sets.
(a) S1 = {(1, 2), (1, 2, 3), (1, 2, 3, 4), ..., (1, 2, 3,..., n)}
(b) S2 = {(1, 2, 3, ..., n-1), (1, 2, 3, ..., n)}
We know that is generated by the
subset of all transpositions in it.
a) Now, observe that
Thus, if
is the subgroup of
generated by
then we have
But then,
for every integers
. That is,
contains all the transpositions in
. Hence,
.
b) Now, observe that
. Thus, if
is the subgroup of
generated by
then we have
But then, for every integers
, we have
for every integers
; this is because
is a transposition as conjugation preserves cycle structure, and
sends
to
. Thus,
contains all the transpositions in
. Hence,
.