0 - 3 of 3 tags for referential integrity

 One of our data modelers came to me with the following scenario.  He is creating two tables and defining a foreign key on one that references the other.
(              ACCT_ID              INTEGER NOT NULL ,
                LOAD_TS              TIMESTAMP NOT NULL

I've found an appendix at the end of TD 13.10's "Temporal Table Support" reference, which contains some SQL code about how can you validating temporal referential integrity shown below. It works great until I want to embed it to a trigger's ...WHEN ( EXISTS (<here>))... section.

I've read the most relevant references from the TD 13.10 documents, but as I see, only soft RI-s are available with temporality - so you must do it yourself...

Which is the most acceptable (and also the simplest) solution maintaining RI's between temporal tables? TRIGGERs?