Proved andb_false

Hadn't bothered before, was really easy, filled it in for completion's
sake
Cleared up problems with Imp

A few things
1) The determinism proof was causing some problem witht he comment and
Abort statement - don't know how, but I fixed it
2) Removed the SearchAbout from a Sn_nle_n
Completed ImpCEvalFun
Started work on Equiv

This chapter is loooong
Also, significantly more difficult