got this error: 'HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
so I did:
1.alter table sp30_subset alter column arrivtime type timestamp using to_timestamp(arrivtime, 'YYYY-MM-DD hh24:mi:ss')::timestamp without time zone;
2.CREATE INDEX idx_sp30_subset_ts_inverse ON sp30_subset (user_id,geom, arrivtime, leavetime DESC);
3.CREATE INDEX idx_sp30_subset_funky ON sp30_subset USING gist (tsrange(arrivtime, leavetime, '[]'));
4.create temporary table mix as (select a.user_id id_x, a.arrivtime arriv_x, a.leavetime leav_x,
h.user_id id_y, h.arrivtime arriv_y, h.leavetime leav_y from ali a, hasan h);
5.select * from mix where tsrange(arriv_y, leav_y,'[]') && tsrange(arriv_x, leav_x,'[]');

## how to call a function in plpgsql:
func: sales_tax()
select sales_tax("pr_id") from sp30_subset;