n 1939, employed in a small municipal library of Buenos Aires where the oafishness of his colleagues made him weep with daily frustration, the 40-year-old (and still largely unknown) Jorge Luis Borges collected a few of the reading notes he had made on the streetcar to and from work, and pieced together a short text which, under the title “The Total Library,” he sent to the magazine Sur, where it appeared in the August issue. The essay, which links the names of Democritus, Lewis Carroll, Cicero, and the forgotten German fantasy writer Kurd Lasswitz, was developed a couple of years later into another, slightly longer one, “The Library of Babel,” which Borges eventually included in his collection “The Garden of Forking Paths” (later expanded under the title of “Ficciones”). The end-paper pages of William Goldbloom Bloch’s “The Unimaginable Mathematics of Borges’ Library of Babel” (Oxford University Press, 192 pages, $19.95) reproduce the first and last pages of Borges’s manuscript, showing that it was written (in what Borges called “the handwriting of a dwarf”) on accounting sheets with the heading Haber, or “Credit,” in Gothic letters that magically make the “H” look like a “B” and the “r” like an “l.”