(string=? string_1 string_2)
(string string_1 string_2)
(string>? string_1 string_2)
(string<=? string_1 string_2)
(string>=? string_1 string_2)

(string-ci=? string_1 string_2)
(string-ci string_1 string_2)
(string-ci>? string_1 string_2)
(string-ci<=? string_1 string_2)
(string-ci>=? string_1 string_2)

The -ci versions are case-insensitive:

> (string=? "Foo" "foo")
#f

> (string-ci=? "Foo" "foo")
#t