Complex query need help with OR condition.

I'm working on a query which works as expected when I leave out one of
the "OR" tests but when the "OR" is included, I get hundreds of
duplicate hits from a table that only contains 39 items. Is there a way
to write the following so that the "WHERE" clause tests for two
possible conditions?

Thanks for any help,

Ken

Here's the working query:

SELECT a.paginator, a.doc_name, (b.time - a.time) as elapsed_time FROM
pm_events as a, pm_events as b
WHERE a.event_code='pmcd'
AND b.event_code='pmcl'
AND a.doc_name=b.doc_name
AND a.paginator=b.paginator
AND a.time < b.time

When I add the OR clause things go haywire:

SELECT a.paginator, a.doc_name, (b.time - pm_events.time) as
elapsed_time FROM pm_events as a, pm_events as b
WHERE a.event_code='pmcd'
OR a.event_code='pmop'
AND b.event_code='pmcl'
AND a.doc_name=b.doc_name
AND a.paginator=b.paginator
AND a.time < b.time

Have also tried the following in the WHERE clause to no avail:

WHERE a.event_code IN {'pmcd', 'pmop'}
WHERE a.event_code=('pmcd' | 'pmop')