第
27
卷第
6
期
No.6
Vo
l.
27
内江师范学院学报
1
JOURNAL
OF
NEUIANG
NORMAL
UNIVERSITY
The
Ko
of
a
Coherent
Polynomial
Extension
ZHAO Wei
*,
WANG Fang-gui ,
SHU
Qian-yu
CInstitute
of
Mathematics
and
Software
Science
,
Sichuan
Normal
University
,
Chengdu.
Sichuan
610068
,
China)
Abstract:
It
is
proved that the polynomial ring
R[t]
over a regular stably coherent ring R
is
also regular,
and
obtained that KoR[tl ,…,t.]
is
isomorphic
to
KoR for any regular stably coherent ring
R.
Key
words: Grothendieck group; coherent ring; regular ring
CLC
number:
0153.3
Doc
ument code: A
o
Introduction
Throughout
this
paper
,
it
is
assumed
that
all
rings
are
commutative
and
associative
with
identity
and
all
modules
are
unitary.
An
important motivation for studying
Grothendied
王
Group
of
regular
polynomial
ring
attributes
to
investigation
to
the
Bass-Quillen
conjecture
,
which
states
that
every
finitely
generated
projective
R[t]-module
is
free
for
any
regular
Noetherian
local
ring
R.
Many
authors
investigate
the
Bass-Quillen
Conjecture
over
Noetherian
and
non-Noetherian
rings
[H4].
The
best
result
on
Bass-Quillen
Conjecture
belongs
to
R.
A.
Rao[IIJ
in
1988
,
who
obtained
that
if R
be
a
regular
local
ring
of
dimension
three
and
residue
characteristic
手
2
,
3
,
then
every
projective
R[t]-module
is
free.
Also
,
many
authors
have
tried
to
investigate
Bass-Quillen
Conjecture
over
non-Noetherian
rings[
IS
oI7
J
.
We
recalled
that
an
R-module
M
is
saided
to
be
stably
free
if M
EB
Rm
R'
for
some
positive
integers
m
and
n.
If
we
denote
the
set
of
all
finitely
收稿日期
:2012
-
02-29
Artict number
:l
671-1785
(2012)06
一
0001
→
04
generated
stably
free R-modules, all finitely generated
projective R-modules and all finitely generated free
R-modules by
SFRM
,
f.
g.
P
R
此
1
and
f.
g.
FreeRM
respectively.
It'
s clear
that
f.
g.
F reeR M C
SF
RM
C
f.
g. PRM.
We
denote
by
R E
PSF
,
R
εSFF
,
while
f.
g.
PRM
SFRM
,
SFRM
f.
g.
Free
RM
respectively.
引
Te
have
that
R
ξPSF
if
and only if
KoR
---....
Z ,
where
Ko is
denoted
by
the
Grothendieck
group
of
R[18].
Thus
the
solution
to
Ko
of
a
coherent
polynomial
extension
is
every
important
to
Ba
ss-Quillen
conjecture over
coherent
rings.
1
Main
resu
It
We
recall
that
a
ring
R is
coherent
,
as
the
generalization
of
Noetherian
ring
, if
and
only
if
every
finitely
generated
submodule
of
a
free
R-module
is
finitely
presented
by
Theorem
2. 3.
2[19J.
We
have
the
following
result
about
the
modules
over
polynomial
ring
R[X]
,
when
the
ring
R
is
coherent.
Theorem
1
Le
t R be a coherent ring and let 0 •
N •
F[
X]
• N
o
•
o
be an exact
R[X]-sequence
,
where
F
is
a
finitely
generated
free
R-module
, N is
基金项目:国家自然科学基金
(11171240
,
11161006)
,四川师范大学定向研究项目(1
0D
泪
,
003)
.
作者简介:赵伟
(1982
一)
,男,四川盾山人,四川师范大学博士研究生.研究方向:交换代数、同调代数,代数
K-
理论与相对同
调的研究.