FINITENESS OF SUBGROUPS OF SELF-HOMOTOPY EQUIVALENCES 3
infinite in terms of the dimensions of the spheres.
Section 2- Minimal Algebras and Rationalization
We begin with some algebraic preliminaries. In general we adopt the conven-
tions of [G-M], [H-S] and [D-G-M-S]. A collection V
=
{Vk
I
k an integer?: 0},
where each Vk is a vector space over the rationals
Q,
is called a graded vector
space. We write v
E
V to indicate that v
E
Vk for some k and let
lvl
denote the
degree
k
of
v.
We shall assume wherever convenient that
V
is finite dimensional.
If v1, ... , Vr is a basis of V, then we write V
= (
v1, ... , Vr).
Let
A
be a differential graded commutative algebra (DG algebra, for short). In
this paper, we only consider DG algebras that have cohomology of finite type, i.e.,
that have cohomology which is finite dimensional in each degree. For a cocycle z
E
A we let [ z]
E
H* (A) denote the cohomology class of z. By a map
f :
A
--+
B of DG
algebras is meant a DG algebra homomorphism. The identity map of
A
will always
be denoted by
~
:
A
--+
A.
If
A
is the free graded commutative algebra generated
by the graded vector space V, then we write
A
=
A(V). If V
= (
v1, ... , Vr), then
A=
A(v1, ... , Vr)·
A DG algebra M is called a minimal algebra if (i) M
=
A(V) for some
vector space V and ( ii) there is a basis v1, ... , Vr, . . . for V such that d( Vr)
E
A(v1
, ...
,vr_
1),
where dis the differential of
M
[G-M]. We denote by
(S)
the
ideal of
M
generated by a subset
S
of
M.
For maps
J,
g :
M
--+
N
of minimal algebras we use the notion of homotopy
given in [H-S,p.240] which we now describe. Suppose M
=
A(V) with differential
d and define a DG algebra M
1
=
A(V EB V EB
V)
with differential also called d
as follows :
V
is an isomorphic copy of V and V is the desuspension of V (i.e.,
vp
=
vp+l ). Furthermore, the differential
d
of
M
1
agrees with the differential on
M, d(v)
=
v and d(v)
=
0, for v
E
V and v
E
V.
In addition, there is a degree
-1 derivation i: M
1
--+
M
1
defined by i(v)
=
v, i(v)
=
0 and i(v)
=
0. We then
obtain a degree 0 derivation
'Y :
M
1
--+
M
1
by setting
'Y
=
di
+
id
=
[d,
i]
(the
bracket of graded derivations). Finally, we have a map
a:
M
1
--+
M
1
defined by
00
1
-'""' n
a-
~~'Y.
n=O
n.
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