left join syntax

I have a database that tracks work orders.  Each order tracks two entries
from the employees table;  the employee ID of the person assigned to the
work order and the ID of the person who completed the order.  Each work
order may have one, both, or neither field filled in.  As such, I need to
left join the employee table to the work order table, but I cannot figure
out the syntax for the double-join.  As independent selects, I can do the
join:

SELECT o.ordr_id, a.last_name
FROM ordr o left join employee a on o.assigned_id = a.emp_id;

SELECT o.ordr_id, c.last_name
FROM ordr o left join employee c on o.completion_id = c.emp_id;

But I would like to have the whole thing in a single SELECT.  Can you help
me out?

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Haywood J'listzen