What does "the repository  does not have a release file" mean?
What can I do if a repository/PPA does not have a Release file?
Programmatically combining images in PHP I'm a big fan of Yahoo's  for speeding up websites. One of the recommendations is to combine images where possible to cut down on size and the number of requests. However, I've noticed that while it can be easy to use CSS sprites for layouts, other image uses aren't as easily combined. The primary example I'm thinking of is a blog or article list, where each blog or article also has an image associated with it. Those images can greatly affect load time and page size, especially if they aren't optimized. What I'm looking for, in concept or in practice, is a way to dynamically combine those images while running them through a loss-less compression using PHP.   A few added thoughts or concerns:   Combining the images and generating a dynamic CSS stylesheet to position the backgrounds of the images might be one way to go about it, but I also worry about accessibility and semantics. As far as I understand, CSS images should be used for layout elements and the img tag (with the alt attribute) should be used for images that are meant to convey information. I could set the image as a background to a div element and substitute a title attribute for the alt attribute, but I'm unsure about the accessibility and semantic implications of doing so. Might the GD library be a good candidate for something like this? Can you recommend other options? Let $f : U \to V$ and $g : V \to W$ be linear transformations on the vector spaces $U$, $V$, and $W$. Supposedly,  $$ \dim(\ker(g \circ f)) = \dim(\ker(f)) + \dim(\ker(g) \cap \operatorname{im}(f)). $$  How might I go about proving that?    (Attempt:) The $\dim(\ker(g)\cap\operatorname{im}(f))$ term suggests to me that I should define a vector space $V' = \ker(g) + \operatorname{im}(f)$ to invoke the theorem that  $$ \dim(V') = \dim(\ker(g)) + \dim(\operatorname{im}(f)) - \dim(\ker(g) \cap \operatorname{im}(f)), $$  but I don't really see where to go from there. Convert .bbl file to .bib file How can I convert a .bbl file to a .bib file. I  lost my .bib file but I still have my .bbl file. Now , I need to add more references to my .bbl file according to a specific format which I need to produce using Bibtex, so how can I convert my .bbl file to a .bib file so I can add the new references according to the format.  Thanks for any insight. Changing text applied when duplicating file in Finder When duplicating files in the finder, OS X attaches a space followed by 'copy' to the file name. This can lead to some file alphabetizing problems and the copies may appear out of order (not directly subsequent to the original). Is there a way to change the appended text? I would prefer that it says '_1' or _copy. Thanks. Ignore citations in captions in list of figures when numbering When using the \cite command in figure captions and the ieeetr bibliography style, then  BibTeX numbers the citations as appearing earlier than they do in reality (i.e. the first citation in the document ends up being [42]).  Is there any way to get BibTeX to ignore the \listoffigures section when numbering? Is there a word for somebody who cares for his/her child too much? I have just finished watching the 3rd season of .  I am wonder whether there is a word for somebody who cares for his/her son/daughter/child too much, like Dr. Cal Lightman? How can I stop being prompted to unlock the 'default' keyring on boot? Whenever Ubuntu boots up, a dialogue pops up asking me to unlock my default keyring. Is there some way this can unlock automatically through PAM or some other magical way? Invisible software updates list in Software Updater Today I received an update notification for three updates but update manager doesn't say what updates are they.    Does anyone have a clue what this is about? How am I to check what is to be updated? Is it possible to use multiple desktop environments on same system? Eclipse returns error message "Java was started but returned exit code = 1" Are the leftovers from making stock good for anything? Having made stock and strained it, can the meat and vegetables boiled up in the stock be used for anything, or should they go in the bin? better Curve/Text to Mesh generation? The triangulation process of Text to Mesh or Curve to Mesh generates some nasty topology.   I get why, but maybe it could be done a bit nicer? Since text is flat, have ngons instead of hundreds of triangles you'll need to modify anyway?  Another issue is when you then want to use the text as a Volume for particles, which for some reason behave weird when you have unusual topology even though they should be using the volume, not vertex or face positions. $\sum (-1)^n/n$ fails the p-series test, but passes the alternating series test? Why do ICs have NC (No Connection or No Function) pins? Take most recent (or concatenate) edit comments when editing during grace period Why is there no analog for $\Theta_\text{QCD}$ for the weak interaction? Is this topological term generated? If not, why not? Is this related to the fact that $SU(2)_L$ is broken? java.lang.NullPointerException at org.glassfish.hk2.classmodel.reflect.impl.TypesImpl.getType Can Mac App Store installs & upgrades be automated? How can I script installing or upgrading apps from the Mac App Store? I'd prefer command line tools, but AppleScript or some other API would suffice.  Relevant puzzle pieces:   installer: note especially the -store flag which is used to simulate App Store installs for package devs. systemupdate: capable of handling updates to Apple apps, flags -i installs and -a tells it to install all available updates What are the strengths and weaknesses of each follower? If you have two envelopes, and ...