12 LOWELL JONES
Lemma 1.4. If cp: Znx£ - £ is a free PL action, leaving invariant each
block b . (£)oof££, thencc p extends toa
which has K a N for fixed point set.
bloc k b . ) f , the n p extend s t o semi-free PL action cp: TL xN - N
Thus to prove Theorem 0.7 of the introduction it suffices to find a
free PL action cp:Z x-£- * £ which leaves the blocks of £ invariant. An
attempt to construct the desired free action on £ is made inthe
following two steps.
Outline of Step 1. In this step the block space £ will be replaced
by a finite CW complex V , containing subcomplexes b.(.£f) l£j£x which
satisfy the following.
1.5. (a) b-CO n b U) = u b U) if and only if b.(C') n b (£') =
! q j
e J
3 i q
u b.(5»)
j€J 3
(b) b^S) n bjCC) ^ 0 if and only if b±W) n b.(V) = 0.
(c) There is a homotopy equivalence f: £ -* £' such that
fi, ^ is a homotopy equivalence b.(.£ ) -* b.C£') for all j.
(d) There is action i| : 2 x£f - * £' which leaves
n
invariant eac h
subcomplexabfree,.cellular
•(£')
The following notation will be used in the rest of this paper.
1.6. (a) £Q is the orbit space of i| : %nxZl + £!
(b) b.(^Q) is the orbit space of ip:Zn*b. C€'} " * b.(£').
(c) If 3b. (C) = U b.U), then 3b.(£'), 3b. ) are defined
J
ieJ
x J J °
as U b.(£') and U b.(£ ) respectively.
i£J J i£J J °
Outline of Step 2. In this step an attempt is made to replace £ ,
and the b.(£ ),by a block space M having PL manifold blocks b.(M ),
such that the following conditions are satisfied.
1.7 (a) There is a homotopy equivalence h: M - * £0 so that hi, (u \
defines a homotopy equivalence b.(M ) b.(£ ) for all l^jf_x.
(b) Let h: M + £f be the n-fold covering of h corresponding to
the covering £f - * £ . Let b.(M) be the n-fold covering of b.(MQ) . There
is PL homeomorphism r: £ •* M satisfying r(.b.(£)) = b.(M) for all j.
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