* liftB and liftB2 imply liftB[3..5] at least ought to exist.

  Really, want something like Applicative. But apparently TypedBehavior
  is not a Functor, and so cannot be Applicative. There might be some
  way to use type classes to do arbitrary arity lifting. Take a look
  at QuickCheck and printf for ideas. Also see
  https://www.seas.upenn.edu/~sweirich/papers/aritygen

  Alternative might be to wrap all of Copilot DSL's functions like (>)
  with ones that operate on TypedBehavior and Event. 
  (Then rename TypedBehavior to Behavior and make everything produce
  and consume that, rather than the underlying Stream?)

  Alternativly, copilot could be improved, see
  https://github.com/Copilot-Language/copilot/issues/56
  https://github.com/Copilot-Language/copilot/issues/59

* using whenB with an input' makes the interpretation see
  each value from the list, even when the whenB is supposed to prevent the
  input' from having run, and the value should be whatever was input
  previously. This may not be fixable w/o Copilot DSL support
  for limiting when inputs happen, at least as far as what the interpreter
  displays as values of the input goes. But, it should be fixable
  as far as the value that is input, at least in theory, by ignoring
  the input values that should not have been input. The  Copilot
  DSL code used to do that may increase the size of the C program
  unncessarily though.