added addD2, addE2, addSD2, and addSE2
improved addbefore and addSbefore
improved mechanism for unsafe wrappers
consts normal :: ifex => bool
primrec
"normal(CIF b) = True"
"normal(VIF x) = True"
"normal(IF b t e) = (normal t & normal e &
(case b of CIF b => True | VIF x => True | IF x y z => False))"