doc-src/Tutorial/Ifexpr/bool2if

added state: 'a * 'b -> 'a * ('a * 'b);

consts bool2if :: boolex => ifex
primrec
"bool2if (Const b) = CIF b"
"bool2if (Var x)   = VIF x"
"bool2if (Neg b)   = IF (bool2if b) (CIF False) (CIF True)"
"bool2if (And b c) = IF (bool2if b) (bool2if c) (CIF False)"