Use PostgreSQL builtin operator <@ after including extension intarray
If you installed the intarray extension to the public schema (or some schema other than pg_catalog), you can schema-qualify the operator to choose the built-in one.

Instead of

a &lt;@ b


you can write

a OPERATOR(pg_catalog.&lt;@) b


to schema-qualify it.

e.g.

test=# SELECT 1 OPERATOR(pg_catalog.+) 2;
 ?column? 
----------
        3
(1 row)