flow.md

"One may also choose to use GNU Parallel (if available) instead of xargs, ..."
Do I have GNU Parallel?

$ man parallel

Something's off. Is there another package?

$ apt-file update
$ apt-file -F search $(which parallel)
moreutils: /usr/bin/parallel
parallel: /usr/bin/parallel

Oh! There are 2 packages. Which one do I have?

$ dpkg -S $(which parallel)
moreutils: /usr/bin/parallel

Ah, and is the other package indeed GNU Parallel?

$ apt-cache show parallel
# ...
Description-en: build and execute command lines from standard input in parallel
 GNU Parallel is a shell tool for executing jobs in parallel using one

Yes!