The CommonPrefix(s1, s2) command returns the length of the longest common prefix of its input strings, s1 and s2.

The actual common prefix can be obtained by indexing into either of the strings, s1 or s2, with the range 1 .. CommonPrefix( s1, s2 ).

Note: String t is a prefix of string s if , for some integer , or t is the empty string. For example, the prefixes of the string "abc" are "", "a", "ab", and "abc".

The CommonSuffix(s1, s2) function returns the length of the longest common suffix of its input strings, s1 and s2.

This function can be defined, in terms of CommonPrefix and Reverse as