13. The evidence that Beethoven occasionally gave away a sketch leaf as a memento is tenuous and vague; nowhere is there the slightest hint that his sketchbooks were ever shared with his musical companions. For a lucid and balanced introduction to the study of the sketches, see Douglas Johnson, Alan Tyson, and Robert Winter, The Beethoven Sketchbooks: History, Reconstruction, Inventory, ed. Douglas Johnson (Berkeley and Los Angeles: University of California Press, 1985), 3–12.