3 check-ins using file docs/weeks/4.md version f2253ea7ca

2022-04-22
09:16
rename default.nix to shell.nix check-in: c5cbf4bc54 user: jboy tags: trunk
09:13
merge revisions for 2022 check-in: 169618ee61 user: jboy tags: trunk
09:02
add week 4 readings Leaf check-in: 8e7f29e025 user: jboy tags: revise-for-2022