I have to deal with unbounded filtrations and want to use the conditional convergence of spectral sequences and the results from 


[1]: *J. Michael Boardman, Conditionally Convergent Spectral Sequences, March 1999 (<http://hopf.math.purdue.edu/Boardman/ccspseq.pdf>)*


The article uses cohomological spectral sequences derived from the exact couple coming from a cochain complex $C$ and a decreasing filtration $F$ of $C$. The system of inclusions is $$A^s := H(F\_s C) \leftarrow A^{s+1}$$ and the pages are denoted by $E^s\_r$ for $s\in \mathbb{Z}$ and $r\in \mathbb{N}$ ($r$ is the page number and $s$ the ``filtration degree''). The symbol $A^\infty$ denotes the limit and the symbol $A^{-\infty}$ the colimit. The symbol $RA^\infty$ denotes the right derived module of the limit. I basically work over $\mathbb{R}$.


The following are the two theorems (or their parts) from [1] which I am interested in:



> 
> **Theorem 6.1 (p.19):** Let $C$ be a filtered cochain complex. Suppose that \begin{equation}\label{Eq:Exit}\tag{C1} E^s = 0\quad\text{for all }
> s>0.\end{equation} If $A^\infty = 0$, then the spectral sequence
>  converges strongly to $A^{-\infty}$.
> 
> 
> **Theorem 7.2 (p.21):** Let $f: C \rightarrow \bar{C}$ be a morphism of filtered cochain complexes and suppose that $E^s$, resp. $\bar{E}^s$
>  converge conditionally to $A^{-\infty}$, resp. $\bar{A}^{-\infty}$.
>  Suppose, moreover, that \begin{equation}\tag{C2} E^s = \bar{E}^s =
> 0\quad\text{for all }s<0. \end{equation} If $f$ induces the
>  isomorphisms $E^\infty\simeq \bar{E}^\infty$ and $RE^\infty\simeq
> R\bar{E}^\infty$, then it induces the isomorphism $H(C)\simeq H(\bar{C})$.
> 
> 
> 


Let me introduce the standard (degree shifted) bigrading on $E\_r$ and visualize $E\_r^{s,d}$ as sitting at the coordinate $(s,d)$ in plane. The differentials are then 
$$ d\_r: E\_r^{s,d}\rightarrow E\_r^{s+r,d-r+1}. $$
My questions are the following:


1. How does Theorem 6.1 generalize if (C1) is replaced by the following **condition of exiting differentials?**
$$ E\_r \text{ sit in a half-plane and if we fix any coordinate }(s,d), \text{ then all but finitely many }d\_r\text{ starting at }(s,d)\text{ leave the half-plane.}$$
2. How does Theorem 7.2 generalize if (C2) is replaced by the following **condition of entering differentials?**
$$ E\_r \text{ sit in a half-plane and if we fix any coordinate }(s,d), \text{ then all but finitely many }d\_r\text{ ending at }(s,d)\text{ start outside of the half-plane.}$$


The author of [1] addresses the questions as follows:


1. On p.19, Chapter 6 in brackets right before Theorem 6.1:



> 
> ...The
>  results generalize appropriately, as all arguments can be carried out degreewise; the
>  main difficulty is to find notation that would help rather than hinder the exposition
> 
> 
>
2. On p.20, Chapter 7 in brackets a couple of paragraphs before Theorem 7.2:



> 
> ...The results remain valid when appropriately modified, as all arguments
>  can be carried out degreewise; the difficulty is to find notation that
>  helps rather than hinders.
> 
> 
>


How do these theorems generalize precisely? Has it been done anywhere? Thanks!


P.S. I come from differential geometry and am not familiar with the proof methods for spectral sequences at all. I use it merely as a black box.



Conditionally convergent spectral sequences with exiting and entering differentials
After a long life in preprint form, Boardman's paper was published in the conference proceedings celebrating his 60th birthday:



```
  \bib{MR1718076}{article}{
       author={Boardman, J. Michael},
       title={Conditionally convergent spectral sequences},
       conference={
          title={Homotopy invariant algebraic structures},
          address={Baltimore, MD},
          date={1998},
       },
       book={
          series={Contemp. Math.},
          volume={239},
          publisher={Amer. Math. Soc., Providence, RI},
       },
       date={1999},
       pages={49--84},
       review={\MR{1718076}},
       doi={10.1090/conm/239/03597},
    }

```

In the $(s,d)$-bigraded case, you can replace Boardman's (left half-plane) condition that $E\_1^{s,d} = 0$ for $s > 0$ (or $s > s\_0$ for some fixed integer $s\_0$) by the (upper half-plane) condition that $E\_1^{s,d} = 0$ for all $d < 0$ (or $d < d\_0$ for some fixed integer $d\_0$).


Similarly, you can replace his (right half-plane) condition that $E\_1^{s,d} = 0$ and $\bar E\_1^{s,d} = 0$ for $s < 0$ (or $s < s\_0$ for some fixed integer $s\_0$) by the (lower half-plane) condition that $E\_1^{s,d} = 0$ and $\bar E\_1^{s,d} = 0$ for $d > 0$ (or $d > d\_0$ for some fixed integer $d\_0$).


This adjustment is often enough. Do you need to refer to other half-planes than those bounded by a horizontal or a vertical line?


EDIT: The OP added some questions, including one about the case of a right half-plane cohomological bicomplex $(B^{i,j}, d\_h, d\_v)$, where $B^{i,j} = 0$ for $i<0$, $d\_h : B^{i,j} \to B^{i+1,j}$ and $d\_v : B^{i,j} \to B^{i,j+1}$. Suppose that $Z^{i,j} \subset B^{i,j}$ is such that $d\_h(Z^{i,j}) = 0$, and filter the total complex
$$
(C, d) = (\bigoplus\_{i,j} B^{i,j}, d\_h + d\_v)
$$
by
$$
F^s = \bigoplus\_{j-i>s} B^{i,j} \oplus \bigoplus\_{j-i=s} Z^{i,j}
$$
for all integers $s$. Here $C$ and $F^s$ are graded, with $B^{i,j}$ and $Z^{i,j}$ in degree $i+j$. Then $(F^s, d)$ is a subcomplex of $(C, d)$, and contains $(F^{s+1}, d)$ as a further subcomplex. We get an exact couple in the usual way, with $A^{s,t}$ and $E\_1^{s,t}$ equal to the degree $s+t$ parts of $H(F^s, d)$ and $H(F^s/F^{s+1}, d)$, respectively.


I claim that $\lim\_s F^s = 0$ and $\lim^1\_s F^s = 0$. This can be checked one degree at a time, since $F^s = 0$ in degrees less than $s$. It follows (see Boardman's Theorem 9.2) that $\lim\_s A^s = 0$ and $\lim^1\_s A^s = 0$, so the spectral sequence is conditionally convergent to the colimit $G = H(C, d)$.


Furthermore, $F^s/F^{s+1}$ and $E^1\_s$ are concentrated in degrees $\ge s$, corresponding to $t\ge0$, so this is an upper half-plane cohomological spectral sequence with exciting differentials. Hence it is strongly convergent to $G$, by the modified form of Boardman's Theorem 6.1 that I mentioned above.


To prove the modified form, one does as Boardman says. Let $F^s G$ be the image of $H(F^s, d)$ in $G$. One must check that the filtration $\{F^s G\}\_s$ of $G$ is complete Hausdorff and exhaustive, and that the natural inclusion $F^s G/F^{s+1} G \to E\_\infty^s$ is an isomorphism. Both claims can be checked one degree at a time, and for each degree the proof of Theorem 6.1(a) carries over. (I do not have Cartan--Eilenberg at hand: I do not recall if they spelled this out.)


