Primitive functions for constructing 4v-sexprs.

Note that all of these operations use hons so that the S-Expressions they produce are structure shared.

These functions carry out a few trivial rewrites (constant folding, double negation elimination). An open question: how much rewriting should they do? Right now I don't try to optimize very aggressively, e.g., 4vs-and doesn't eat bufs. It's not clear how much of the code from sexpr-rewrite should be duplicated here.

- 4vs-not-list
`(4vs-not-list x)`maps 4vs-not across a list.- 4vs-onehot
`(4vs-onehot sexprs)`constructs an s-expression that isT when the members ofX are one-hot.- 4vs-ite*-list-dumb
`(4vs-ite*-list-dumb c as bs)`produces a list of sexprs, basically(4V-ITE* C Ai Bi) for the corresponding elements ofAS andBS .- 4vs-and-list-dumb
`(4vs-and-list-dumb sexprs)`reduction ands together all the sexprs in the listx , producing a single sexpr representing their conjunction.- 4vs-not
`(4vs-not a)`constructs a 4v-sexpr equivalent to(not a) .- 4vs-and-list
`(4vs-and-list sexprs)`reduction ands together all the sexprs in the listx , producing a single sexpr representing their conjunction.- 4vs-and-dumb
`(4vs-and-dumb a b)`constructs exactly the 4v-sexpr(and a b) .- 4vs-and
`(4vs-and a b)`constructs a 4v-sexpr equivalent to(and a b) .- 4vs-zif-dumb
`(4vs-zif-dumb c a b)`constructs(ZIF C A B) , i.e., the s-expression for an pass-gate style multiplexor.- 4vs-z
`(4vs-z)`returns(Z) , the s-expression for a constant undriven/floating value.- 4vs-x
`(4vs-x)`returns(X) , the s-expression for a constant unknown value.- 4vs-t
`(4vs-t)`returns(T) , the s-expression for a constant true value.- 4vs-ite*-dumb
`(4vs-ite*-dumb c a b)`constructs(ITE* C A B) , i.e., the s-expression for a conservative multiplexor.- 4vs-f
`(4vs-f)`returns(F) , the s-expression for a constant false value.- 4vs-iff
`(4vs-iff a b)`constructs a sexpr representing(iff a b) .- 4vs-buf
`(4vs-buf a)`constructs a 4v-sexpr equivalent to(buf a) .- 4vs-xor
`(4vs-xor a b)`constructs a sexpr representing(xor a b) .- 4vs-or
`(4vs-or a b)`constructs a 4v-sexpr equivalent to(or a b) .- 4vs-implies-lists
`(4vs-implies-lists x y)`pairwise impliess together the sexprs from the lists x and y, forming a new sexpr list.- 4vs-implies
`(4vs-implies a b)`constructs a new sexpr representing(implies a b) .- 4vs-xor-lists
`(4vs-xor-lists x y)`pairwise xors together the sexprs from two separate lists, forming a new sexpr list.- 4vs-or-lists
`(4vs-or-lists x y)`pairwise ors together the sexprs from two separate lists, forming a new sexpr list.- 4vs-or-list
`(4vs-or-list x)`reduction ors together all the sexprs in the listx , producing a single sexpr representing their disjunction.- 4vs-iff-lists
`(4vs-iff-lists x y)`pairwise iffs together the sexprs from the lists x and y, forming a new sexpr list.- 4vs-and-lists
`(4vs-and-lists x y)`pairwise ands together the sexprs from two separate lists, forming a new sexpr list.