STRING<
=======

Syntax: (string< <string1> <string2>
          :START1 <number> :END1 <number>
          :START2 <number> :END2 <number>)

This function compares (parts of) strings with
differentiation between upper- and lowercase-
characters. It returns the length of the common
begin-part, when the strings are equal, otherwise
NIL.

examples:      >(string< "Auto" "Automobil")
               4

               >(string< "Automobil" "Auto")
               NIL