This is a personal project by @dellsystem. I built this to help me retain information from the books I'm reading.
Source code on GitHub (MIT license).
de Botton, A. (1997). How to be Happy in Love. In de Botton, A. How Proust Can Change Your Life. Picador, pp. 159-172
an unfilled space; a gap (plural: lacunae)
the lacuna in her knowledge of art history