I made a mistake, believing that `ag` could handle extended glob syntax. The real numbers are:

    ~/src/racket/racket/share/pkgs$ find . -iname '*.rkt' | xargs ag lambda | wc -l
    33589

    ~/src/racket/racket/share/pkgs$ find . -iname '*.rkt' | xargs ag λ | wc -l
    16722

Glyph λ is more common than I thought, but still heavily outnumbered by spelled-out lambda.