KMP calculates the boundaries of all string prefixes, which themselves are a key concept in the string algorithm. (Computing the boundary of an entire word is itself nontrivial, and KMP (rejection function) is the standard for this!)
The border s is simply any word that is both the prefix and suffix s.
, w , k w ^ k = s s. s.
. s - w s, s wwww... , abc - abcabcab. , 1:1 ; , abcab abcabcab. , w s, , s w (w ^ -1 s), s. , w s, , s, w, s.
. , , () ; . .