The Universe's existing has a finite-past (Or: The serried number of events earlier than now are merely finite in quantity).
This is relevant because if the number of events earlier than now are merely finite, then there must be a first event (as defined in the introduction).
The standard Hot Big Bang model is true. This is relevant because if the Hot Big Bang model is true, then at some finite point in the past, the Universe suddenly came into existence (thereby beginning to exist).
The Universe's existing has an infinite-past (Or: The serried number of events earlier than now are infinite in quantity). This is relevant because if the past serried number of events are infinite, then there is no first event, and so presumably there is no beginning.
[Brackets] mean “Forthcoming.”
The B-theory of time is true. This is relevant because it would mean that any coming into being of the Universe would be a “tenseless fact.” (This in turn is relevant because Craig analyzes “begins to exist” in a way that requires the fact reporting the Universes' coming into being to be a tensed fact).
The initial cosmic singularity is merely a point on the boundary of space-time, rather than a first temporal point in it This relevant because if the Universe has no beginning point, then arguably it has no beginning.
But, so what if there is no beginning point? Couldn't it still be that a past event nevertheless occupies a first duration (i.e. nonzero finite temporal interval which was absolutely first—not preceded by any equal interval.)? This would be sufficient for the Universe having a beginning.1