1. A method comprising: (a) receiving one or more sequences of digital data into a provided memory; (b) the computation of a numerical similarity signature, referred to as the equivalence signature, for a sequence of digital data, as a sum over the number of subsequences that constitute said sequence of digital data with each summand being positive one if the value of the fundamental homotopy group's invariant for the values of the elements of a subsequence is even, and negative one if said value of the fundamental homotopy group's invariant for said values of the elements of said subsequence is odd; (c) the computation of said fundamental homotopy group's invariant of a subsequence as the difference between the last and first values of said subsequence; and (d) the computation of a similarity distance between any two sequences of digital data as the absolute value of the difference of their equivalence signatures so that said similarity distance will either be equal or differ by a bounded value that is less than the lesser of the two numbers of subsequences in said sequences of digital data.