Here are few examples from PostgreSQL-9.5
Display list:
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Display Definition:
postgres=# \sf
function name is required
postgres=# \sf pg_reload_conf()
CREATE OR REPLACE FUNCTION pg_catalog.pg_reload_conf()
RETURNS boolean
LANGUAGE internal
STRICT
AS $function$pg_reload_conf$function$
postgres=# \sf pg_encoding_to_char
CREATE OR REPLACE FUNCTION pg_catalog.pg_encoding_to_char(integer)
RETURNS name
LANGUAGE internal
STABLE STRICT
AS $function$PG_encoding_to_char$function$