[44-3] exercise designed to see cp as a self-contained
module:
use cp to the get the 1st part of conjunction; use the
conditional as a premise to get the 2nd part; & be
careful not to take the 2nd part of conjunction from cp
c: (h -> m) & ~f
1: ~h v ~f
2: ~m -> f
3: (~h v m) -> ~f