What sort of argument is that? If the Duet Display author wasn't able to find the GPL license for CocoaSplit, how could he assume that the code was available for any use? Furthermore, the ISC and BSD licenses of PeerTalk and GPUImage are rather permissive, yes, but they do require attribution that is not given by Duet Display.

The big deal here is that licenses matter, especially when you're profiting from others' work.

> And who amongst us has grepped for a license?

Try packaging some software for Debian and you'll do a lot of grepping because Debian cares deeply about complying with the law. I've also poked Red Hat's lawyers to get some kernel code from GPLv2 to GPLv2+ because I wanted to reuse it in GPLv3 software, etc. If you're following the law, you're grepping for licenses. If you or your employer don't care about complying with the law, you're welcome to take that risk.

Here's the results of all the grepping I did for a Debian package recently, and this was relatively straightforward as software goes. Note the lines that start "Comment": https://tracker.debian.org/media/packages/p/prelink/copyrigh...

If you don't have the explicit right to reuse a piece of code, you can't assume you do. If you don't like this, get your lawmakers to remove your country from the Berne Convention. Or you can risk breaking the law and hope nobody notices; up to you.

It might be telling that there's an entire _company_ dedicated to grepping for licenses as a service, because people don't do so and then they get in trouble. https://www.blackducksoftware.com/

If there's no license then you can't incorporate the code at all. "It's hard to find the license" is not an argument. If you can't find it then you have to assume you can't use it.

The source headers say it's copyright and all rights reserved. Even without this notice you would have to presume a full copyright.