Fix subtle bug in ~_E computation

Fix subtle bug in ~_E computation

The computation for the action ~_E requires
that we compute whether `p` is independent with
some sequence of transitions `w` after an
execution `E`. The algorithm for computing
whether an equivalent trace was found works
to iteratively eliminate events from the
equivalent sequence, leaving behind only
the remaining "bits" that are needed for
insertion into a wakeup tree.

The bug involved a typo of `w` for `w_now`
:( :( which broke everything :/