ScholarLy newbie, running annotate.ly, gets error message

[Graham King]

excuse the haiku!

In my first attempt at using ScholarLy, I'm trying to compile the supplied example, openlilylib/ly/scholarly/usage-examples/annotate.ly

The include path for Frescobaldi 2.18.1 is:
>     /Users/grahamk/Documents/lilypond/include_gk
>     /Users/grahamk/Documents/lilypond/music/openlilylib
>     /Users/grahamk/Documents/lilypond/music/openlilylib/ly
>     /Users/grahamk/lilypond/include
At compile time, the lilypond log starts:

>     Starting lilypond 2.19.21 [annotate.ly]...
>     
>     Processing `/Users/grahamk/Documents/lilypond/music/openlilylib/ly/scholarly/usage-examples/annotate.ly'
>     
>     Parsing...
>     
>     openLilyLib: library infrastructure successfully loaded.
>     
>     /Users/grahamk/Documents/lilypond/music/openlilylib/ly/scholarly/usage-examples/annotate.ly:5:1: warning: openLilyLib: Library main file "/Users/grahamk/Documents/lilypond/music/openlilylib/ly/scholarly/__main__.ily" not found
>     
>     \useLibrary ScholarLY
>     
>     /Users/grahamk/Documents/lilypond/music/openlilylib/ly/scholarly/annotate/__main__.ily:50:1: warning: openLilyLib: Library main file "/Users/grahamk/Documents/lilypond/music/openlilylib/ly/utility/__main__.ily" not found
However, both files are there:
>     $ ls -l /Users/grahamk/Documents/lilypond/music/openlilylib/ly/{scholarly,utility}/__main__.ily
>     -rw-r--r--  1 grahamk  staff  2140 17 Oct 22:36 /Users/grahamk/Documents/lilypond/music/openlilylib/ly/scholarly/__main__.ily
>     -rw-r--r--  1 grahamk  staff    37 17 Oct 22:36 /Users/grahamk/Documents/lilypond/music/openlilylib/ly/utility/__main__.ily
Can anyone identify the no-doubt humiliatingly-obvious error that I've committed?

TIA,
-- Graham