scanning – How do I keep my paper perfectly flat on flatbed scanner?

I am scanning a photobook, I have unbinded the book and scanning the pages one by one to my Epson Perfection v600. The problem I ran into is that the pages couldn’t lay completely flat on the bed, the pressure from the cover was not strong enough. It was okay for individual pages as they are not that noticeable but it became a problem when I have pages that needs to be stitch together in Photoshop, I have a hard time aligning them.

I tried putting credit card size cards on top of the paper but they were just way too small to cover the entire page. What other methods can I do?

Gimp insists on changing Epson SC-P800 black to photo black on plain paper

I’m trying to print an image on plain paper with an Epson SC-P800 printer using GIMP 2.10 on MacOS 10.14.6 (Mojave). I can find no setting in the print or page-setup dialogs to set which black ink is used. When I attempt to print the printer is prompting me to switch to Photo Black.

Has anyone made this work?

film – Can a LCD projector imprint an image onto a light-sensitive paper?

I am trying to develop an experiment in which I would expose a fast-framed video (almost timelapse-y) to a light-sensitive paper for a short amount of time as in the same process used to make photograms. However, I do not own an analog projector and I was wondering if it would work with a regular LCD projector. I have run a few experiments on a scanner, but unfortunately the light of projection and the light used by the scan to capture the image mostly cancelled itself out, due to the LCD nature of both, resulting in an overexposed image with a few dashes of what the projection was. Considering analog procedures don’t use that kind of light information, I thought it could work.

What do you think?

bitcoin core – What needs to be written down for a paper wallet?

I’m installing bitcoin-core with snap on Ubuntu for a dry-run at generating a paper wallet.

Perhaps naively, I thought to “write down” something like:

nicholas@mordor:~/bitcoin$ 
nicholas@mordor:~/bitcoin$ ls
nicholas@mordor:~/bitcoin$ 
nicholas@mordor:~/bitcoin$ ssh-keygen -t ed25519 -C saunders.nicholas@gmail.com
Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/nicholas/.ssh/id_ed25519): ./bitcoin_wallet
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in ./bitcoin_wallet
Your public key has been saved in ./bitcoin_wallet.pub
The key fingerprint is:
SHA256:MtZQUFLqDWU0fJbkFhner+ZRF1WZ1MacM0WOBbGPvCc saunders.nicholas@gmail.com
The key's randomart image is:
+--(ED25519 256)--+
|      o*O.++  +B&|
|       *.+=o   @*|
|      +  o+ . oo+|
|     . = .   o o.|
|      = S     = o|
|     . o     o o |
|            + E .|
|           o . o |
|            .    |
+----(SHA256)-----+
nicholas@mordor:~/bitcoin$ 
nicholas@mordor:~/bitcoin$ ls
bitcoin_wallet  bitcoin_wallet.pub
nicholas@mordor:~/bitcoin$ 
nicholas@mordor:~/bitcoin$ cat bitcoin_wallet
-----BEGIN OPENSSH PRIVATE KEY-----
b3...AAtzc2gtZW
QyNTUxOQAAACD...AAAKBLLY/ISy2P
yAAAAAt...jpB6ZXAZLiLoXx+D9kw
AA..JYB62mUlxCESA
KyOkHp...LmNvbQEC
-----END OPENSSH PRIVATE KEY-----
nicholas@mordor:~/bitcoin$ 
nicholas@mordor:~/bitcoin$ cat bitcoin_wallet.pub 
ssh-ed25519 AAA..IuhfH4P2T saunders.nicholas@gmail.com
nicholas@mordor:~/bitcoin$ 

where I need the public and private key. Obviously, very easy to make a mistake, but isn’t that what’s required??

I’m not understanding all this mention of writing down seed words or passphrases. Isn’t the key pair required?


leaving aside QR codes or other automated tools for storing keys.

signature – How can I sign a bitcoin address that is on a paper wallet?

I have a bitcoin address that shows I held the BTC prior to December 2019. I need to verify this but as the address refers to a paper wallet I don’t seem to be able to do so. If I move the coin to a hardware/software wallet I can verify BUT I will have created a new address that doesn’t meet the criteria in that case.

Is there a way to sign a message with my paper based bitcoin address? Or import the paper wallet into something that can sign messages?

riemannian geometry – Is there are mistake in this paper?

This is kind of a strange and vague question… sorry about that.

I am really interested in $G_2$ Twisted Connected sums as described in this paper: https://arxiv.org/abs/math/0012189 “Twisted connected sums and special Riemannian holonomy” by Alexei Kovalev. I would like to use those constructions to come up with examples to test new ideas.

Some people have told me that this paper is “not taken seriously” because there are mistakes in it. These people were not sufficiently familiar with the paper to tell me what the mistakes were and whether or not they had been corrected.

I have found maybe one or two mistakes but they are very small. More like typos.

Does anyone here know what the “mistakes” are (if there are any) or what the story is behind these rumors?

ct.category theory – Are generators defined in Tohoku paper equivalent to that defined in Wikipedia (Which I believe is a more widely used definition)

As I was reading Grothendieck’s Tohoku paper(translated by M.L.Barr and M.Barr), I found that the definition of a generator in the category differs from that defined in wikipedia.
Let $mathbf{C}$ be a category(It may be necessary that $mathbf{C}$ is a locally small category), a family of generators {$U_i$}$_{iin I}$ with $I$ being an index set, according to Tohoku paper, are a collection of objects such that for any object $A$ and any subobject $B neq A$, there is $iin I$ and a morphism $ucolon U_i rightarrow A$ which does not come from $U_i rightarrow B$. While in wikipedia, it is defined in a way such that for any $f,gcolon Arightarrow B$ with $fneq g$, there is an $iin I$ and $ucolon U_irightarrow A$, such that $fcirc u neq gcirc u$.
What I would like to know is that are these 2 definitions equivalent, or is the definition in Wikipedia stronger than that in Tohoku paper?

ac.commutative algebra – A small lemma in Schlessinger’s criterion paper

In the construction of a hull in Schlessinger’s paper, one small lemma used is not clear in my opinion. That should be stated as follows:

Let $(R,m)$ be a Noetherian complete local ring, $I_1supset I_2supsetcdots$ be a descending chain of proper ideals such that $I_n$ contains $m^n$. Let $I$ be the intersection of all $I_n$. Then for every $kin mathbb{N}$, there is a $n(k)$ such that $m^k+I$ contains $I_{n(k)}$.

What I did was consider the inverse system ${(m^k+I_n)/(m^k+I)}_{n,k}$ and compute the inverse limit in two different ways. $R/m^k$ is Artinian is used and the condition that $I_n$ contains $m^n$ can be dropped. But I feel like there should be more direct ways to prove this. Are there any easier or instant proof for this?