4.1.9. GNATCOLL.Damerau_Levenshtein_Distance

function GNATCOLL.Damerau_Levenshtein_Distance is
  new GNATCOLL.Damerau_Levenshtein_Generic (Character, Positive, String);
--  Damerau Levenshtein distance between L and R strings.
--  Calculated in minimum number of elementary operations to convert one
--  string to another. The operations are deletion, insertion, substitution,
--  and transposition (swap 2 adjacent characters).