$ nix develop
# Navigate to the top-level Leios folder.
$ cd .../ouroboros-leios
$ cabal update
$ cabal build allBuild xyz among the following . . .
agdaIOGPreludeagdaSetsagdaStdlibagdaStdlibClassesagdaStdlibMetaagdaWithDepsleiosSpecols
. . . with the command . . .
$ nix build .#xyz$ nix run .#ols -- --help