I posed this question to [another user][1], but we weren't able neither to make a precise guess, nor to give a precise proof. Is it a "not-so-well" well-known fact?

Consider a connected non-finite CW complex $X$; denote its Poincare' series as $p_X(T)=a_0+a_1T+\dots + a_nT^n+\dots$

Since $X$ is connected, the series $p_X(T)$ is an invertible element in $\mathbb Z[\![T]\!]$: what is the geometric meaning of its inverse series $q(T)$? Can it arise as the series of a space $Y$?  Which is the relation between $X$ and $Y$?


**Edit**:
As it was pointed out in the comments, the question as it is stated makes no sense: whatever the series $p_X(T)$, its inverse will have *negative* coefficients, so there is no way to interpret them as dimensions of homology objects associated to a wouldbe space $Y$.

Nevertheless, there are cases where utterly counterintuitive statements like "there is a [groupoid][2] whose measure is $\sum_k \frac{1}{k!}$" have suitable meaning. So my question sounds more like 

> is there a "groupoidal-trick" to turn the (multiplicative) inverse Poincare' series into something meaningful, by stretching a bit the meaning of the word "space"?


  [1]: http://mathoverflow.net/users/8320/domenico-fiorenza
  [2]: http://ncatlab.org/nlab/show/groupoid+cardinality