Updating a table via a view

I am trying to maintain a history of rows. The base table has a start
and end date. I am updating the table using a view and a rule.  The
rule, updates the end date on the current record and then inserts a new
row with the modified columns, or at least thats what I want to happen.

The update is occuring but the insert doesn't.  I get no error but no
row. The rule looks like this;

CREATE RULE a_update
    AS ON UPDATE TO a DO INSTEAD
        (UPDATE a_hist
            SET tend = now()
            WHERE (a.x = old.x)
              AND (a.tend = 'infinity'::timestamptz);
         INSERT INTO a_hist (
            x,
            tstart,
            tend,
            y,
            z
         ) VALUES (
            new.x,
            now(),
            'infinity'::timestamptz,
            new.y,
            new.z
         );
        );

Any pointer as to what I am doing wrong ?

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