In 1966, Vladimir Levenshtein introduced the notion of the edit distance
between two strings as the minimum number of editing operations needed
to transform one string into another, where the edit operations are insertion
of a symbol, deletion of a symbol, and substitution of one symbol for another.
For example, TGCATAT can be transformed into ATCCGAT with five editing
operations, shown in figure 6.11. This implies that the edit distance between
TGCATAT and ATCCGAT is at most 5. Actually, the edit distance between
them is 4 because you can transform one to the other with one move fewer,
as in figure 6.12.