  We investigate two types of temporal symmetry in quantum mechanics. The first
type, time symmetry, refers to the inclusion of opposite time orientations on
an equivalent physical footing. The second, event symmetry, refers to the
inclusion of all time instants in a history sequence on an equivalent physical
footing. We find that recent time symmetric interpretations of quantum
mechanics fail to respect event symmetry. Building on the recent fixed-point
formulation (FPF) of quantum theory, we formulate the notion of an event
precisely as a fixed point constraint on the Keldysh time contour. Then,
considering a sequence of measurement events in time, we show that both time
and event symmetry can be retained in this multiple-time formulation of quantum
theory. We then use this model to resolve conceptual paradoxes with time
symmetric quantum mechanics within an `all-at-once', atemporal picture.
