Figure 1(a): Block-sorted text. Start with the source string "abracadabra." Append an end-of-file metacharacter $, with the property that $<a-z. Cyclically shift the string from 0 to n-1 places, and sort the resulting list. Each row is called a "block," containing original text left-shifted 0 to n-1 places. M is the 12×12 block-sorted matrix for string "abracadabra$," F is the first column of the matrix, L is the last column.