selecting from integer[]

select * from pg_user where usesysid=(select grolist[1] from pg_group 
where groname='mygroup');
select * from pg_user where usesysid=(select grolist[2] from pg_group 
where groname='mygroup');
select * from pg_user where usesysid=(select grolist[3] from pg_group 
where groname='mygroup');

Can those three queries be merged to one query? (and still gives me 
those three rows)
Or do I have to explicitly say grolist[1], grolist[2], etc....

Thanks in advance :)