Low-level functions for constructing faigs.

These functions construct new FAIGs from existing ones. They typically honsing up some new onset and offset aigs by using the using aig-constructors like aig-and and aig-not, and then cons those new onset/offset AIGs together to form a new FAIG.

Most of these functions are geared toward modeling hardware. For instance, f-aig-and is intended to produce a new FAIG that captures the four-valued logic semantics of an AND gate.

Note: the details about how X and Z are handled by these functions are
often subtle and this documentation doesn't really explain *why* these
functions work the way they do. **However**, for most functions here there
are corresponding 4v-operations, and the documentation there typically
*does* explaining the X/Z behavior.

There is an important optimization you can make when modeling hardware gates as FAIGs. In particular, it is often possible to construct more efficient (smaller) FAIGs to represent the gate's output when you know that the gate's inputs cannot evaluate to Z.

In CMOS designs, this property—never evaluating to Z—holds for
the outputs of most logic gates. Accordingly, it's true for most *inputs*
to other gates. For example, suppose you are trying to model a circuit like
this:

|\ b ---| >o---+ |/ | ____ +------| \ | | and )--- ---| >o----------|____/ o |/ a

Here, we know that wires *and* gate, where we assume that our inputs are
non-Z.

Of course, some logic gates (e.g., tri-state buffers) *can* produce Z
valued outputs, so occasionally these sorts of optimizations aren't possible.
Because of this, we typically have two versions of each FAIG constructor:

t-aig-* functions make the assumption that their inputs are can never evaluate to Z. These are generally more efficient, and will produce smaller AIGs that are easier to analyze with SAT solvers.f-aig-* functions do not make this assumption. This makes them more general purpose and able to operate on any FAIG inputs, at the cost of larger AIGs.

For historic reasons these functions are left enabled. There are two useful rulesets you can use to disable them:

f-aig-defs has all of thef- constructors.t-aig-defs has all of thet- constructors.

- T-aig-ite*
`(t-aig-ite* c a b)`constructs a (more conservative) FAIG representing(if c a b) , assuming these input FAIGs cannot evaluate to Z.- T-aig-ite
`(t-aig-ite c a b)`constructs a (less conservative) FAIG representing(if c a b) , assuming these input FAIGs cannot evaluate to Z.- F-aig-ite*
`(f-aig-ite* c a b)`constructs a (more conservative) FAIG representing(if c a b) , assuming these input FAIGs cannot evaluate to Z.- F-aig-ite
`(f-aig-ite c a b)`constructs a (less conservative) FAIG representing(if c a b) .- T-aig-tristate
`(t-aig-tristate c a)`constructs an FAIG representing a tri-state buffer whose inputs are known to be non-X.- F-aig-zif
`(f-aig-zif c a b)`constructs an FAIG representing a kind of pass gate style mux.- T-aig-xor
`(t-aig-xor a b)`*xor*s together the FAIGsa andb , assuming they cannot evaluate to Z.- T-aig-or
`(t-aig-or a b)`*or*s together the FAIGsa andb , assuming they cannot evaluate to Z.- T-aig-iff
`(t-aig-iff a b)`*iff*s together the FAIGsa andb , assuming they cannot evaluate to Z.- T-aig-and
`(t-aig-and a b)`*and*s together the FAIGsa andb , assuming they cannot evaluate to Z.- F-aig-and
`(f-aig-and a b)`*and*s together the FAIGsa andb .- F-aig-xor
`(f-aig-xor a b)`*xor*s together the FAIGsa andb .- F-aig-or
`(f-aig-or a b)`*or*s together the FAIGsa andb .- F-aig-iff
`(f-aig-iff a b)`*iff*s together the FAIGsa andb .- F-aig-res
`(f-aig-res x y)`constructs a FAIG that represents the result of connecting two (independently driven) wires together.- F-aig-unfloat
`(f-aig-unfloat a)`converts floating (Z) values to unknown (X) values.- F-aig-pullup
`(f-aig-pullup a)`constructs an FAIG representing a pullup resistor.- T-aig-not
`(t-aig-not a)`negates the FAIGa , assuming that it cannot evaluate to Z.- F-aig-not
`(f-aig-not a)`negates the FAIGa .- T-aig-xdet
`(t-aig-xdet a)`constructs an FAIG for 4v-xdet, assuming that the argumenta cannot evaluate to Z.- F-aig-xdet
`(f-aig-xdet a)`constructs an FAIG for 4v-xdet.