order by, within a plpgsql fx

Please consider this plpgsql function:
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CREATE Or Replace FUNCTION fx_order_by ( )
RETURNS table( last_name text, first_name )
AS $eofx$
DECLARE
--
BEGIN

  Return Query
  select
    lname, fname
  from
    my_table
  order by
    lname  ASC
  ;

END;
$eofx$ LANGUAGE plpgsql;
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So, is this select statement's result set  guaranteed to be ordered as specified by the [order by] coded within the
functionbody ? 
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select last_name, first_name from fx_order_by() ;
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Or, must I code another [order by] to be sure ?
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select last_name, first_name from fx_order_by()   order by last_name ;
= = = = = = = = = =

Also, is the answer the same for a "sql" function ?

Thanks,
-dvs-