&quot;Jingle bells, Batman smells, etc&quot; -- any copyright or trademark problems in that now-famous song lyric? &quot;Jingle bells, Batman smells, Robin's laid an egg&quot; -- any copyright or trademark problems, per se, in that now-famous song lyric?
The original Jingle Bells song was first published as a Thanksgiving Song in 1857 and has lapsed into public domain. The Batman lyrics constitute parody which would further put their singing under fair use. You may sing it as part of your own musical arrangement with little discourse from Warner Bros, the current copyright holders of Batman and related properties OR the original parody lyricist, who has not to my knowledge done anything to protect his copyright claim to the song. You may not sell the version of the Batman version as sung by Mark Hamil in the 1992 Batman: The Animated Series episode &quot;Christmas with the Joker&quot; without permission of Warner Bros.
A character can not be copyrighted. Only a work (picture, text, movie etc.) featuring that character can. However, a character can be registred as a trademark (more specifically, its name and its appearance).
One reason could be because of the scènes à faire doctrine. Many of the things you notice as similarities are not infringement. I don't know the counts of lawsuits for music infringement vs screenwriting infringement. There may just be more songs than screenplays. Screenwriters/producers do get sued, though. See Cinar Corporation v. Robinson 2012 SCC 25.
Details depend on the juristiction. For that, consult a lawyer if you plan to publish your app anywhere. But generally, even simple texts from exercises can be covered by copyright. Compare song lyrics, which are not much longer (and might not involve more creative thought than a good exercise ...). For vocabulary lists, it gets more tricky, but those can be covered as well if the assembly of the list was a creative effort. So if you simply list the 1,000 most common worlds in English and their translation, you are possibly fine, but if the words are divided into units and lessons, that's creative work.
As you've presented them, I doubt the functions are protected by copyright in the first place. Originality is one of the threshold requirements for copyright protection, and it demands that the work in question be independently created by the author, and that it possess some minimal degree of creativity. If you're talking about programming at a level so basic that the function truly must be created in a particular way, there is no originality in simply following the instructions. And even if there's some wiggle room, but the language you used has likely been independently replicated by many programmers, that's still not original enough to be copyrightable. What you want to watch out for, though, is the possibility that they've been combined into an original arrangement that is protected. I don't know enough about how copyright law is applied to code to say where or how that line is drawn, but my instinct would be that it could be a fairly low threshold.
Plagiarism is an academic concept, not a legal one. The issue you are concerned about is copyright infringement. A work based off of another copyrighted work is a derivative work. This requires permission of the copyright holder. Simply listing your source and saying &quot;no crime intended&quot; does not help. However, recipes are generally not copyrightable (at least in the UK/US). This is because they are a list of ingredients and instructions which is not sufficient for a creative work. The presentation of the recipe can be copyrighted, as can any descriptive text surrounding it. If you're just taking the actual recipe, making a better recipe from it, and presenting that recipe in a better way, you should be fine.
Ideas are not protected by copyright, only arrangements of words are protected. If you &quot;rephrase&quot; by only a minor change of wording, leaving much of the wording intact, that is still a copyright infringement unless an exception such as fair use or fair dealing applies (and that seems a bit doubtful in this case). If you &quot;rephrase&quot; so that the wording is quite different, even though the idea is the same, there is probably no infringement. Copying elements of computer code or other IT commands that are essential to making an example work is not infringement. Where there is only one or a very small number of ways to naturally express a fact, copying such expression is not infringement, as facts are not protected by copyright. Adding examples but keeping significant wording unchanged is still likely to be infringement.
It doesn't make a difference if the product is free or commercial use, if it's initiated by a company or an individual. What you are considering would be a &quot;derivative work&quot; and without explicit permission from the copyright holder, it is considered a violation.