linux.sql

SELECT version();
                                                             version
----------------------------------------------------------------------------------------------------------------------------------
 PostgreSQL 11.5 (Debian 11.5-1.pgdg90+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516, 64-bit
(1 row)

-- Why is this returning true?
-- I think { and [ are considered to sort equally on this machine's `en_US` collation, 
-- so the result is the same as `'{' < '{a'`
SELECT '{' < '[a' COLLATE "en_US";
 ?column?
----------
 t
(1 row)

SELECT '{' < '[a' COLLATE "C";
 ?column?
----------
 f
(1 row)

macos.sql

SELECT version();
                                                   version
-------------------------------------------------------------------------------------------------------------
 PostgreSQL 11.5 on x86_64-apple-darwin16.7.0, compiled by Apple LLVM version 8.1.0 (clang-802.0.42), 64-bit
(1 row)

SELECT '{' < '[a' COLLATE "en_US";
 ?column?
----------
 f
(1 row)

SELECT '{' < '[a' COLLATE "C";
 ?column?
----------
 f
(1 row)