zipper_algebra: Add XOR#42
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…n the original slice-of-slices version Everything is now expressed in terms of two bounded bitspaces
Introduce zipper_merge_dnf(), a generalized trie merge capable of
evaluating monotone Boolean expressions in Disjunctive Normal Form.
The implementation represents a DNF as:
(Clause0) ∨ (Clause1) ∨ ...
where each Clause is a conjunction of input zippers encoded as a
compact bitmask. This replaces the earlier slice-of-slices approach
with a fixed universe of zippers plus clause membership masks.
Highlights:
* Add Clause<N> newtype for conjunction representation.
* Enforce clause validity at construction time.
* Add clause![] helper macro for ergonomic DNF construction.
* Share zipper traversal across clauses that reference the same input.
* Perform iterative tail descent when all active clauses follow the
same path.
* Dispatch single-clause cases to specialized meet implementations.
* Support arbitrary monotone DNF expressions, including majority and
threshold functions.
Example:
(x ∧ y) ∨ (x ∧ z) ∨ (y ∧ z)
can now be expressed as:
[
clause![0, 1],
clause![0, 2],
clause![1, 2],
]
and evaluated directly via zipper_merge_dnf().
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… bits directly" This reverts commit 0c8ca25.
zipper_algebra: Implement majority-of-three using DNF zipper merge
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This change introduces an n-way XOR operation implemented on top of the
existing ordered zipper traversal framework.
The implementation treats tries as sparse path→value mappings, with missing
paths interpreted as the lattice bottom element. XOR is therefore computed
pointwise on values rather than on path presence:
A deliberate design choice is that traversal follows join semantics: a child
edge is explored whenever it is present in at least one input. Although XOR is
often described in terms of parity, cancelling values at a path does not imply
that all descendants cancel as well. Stopping traversal based solely on path
parity would therefore miss surviving values in deeper subtries.
As a result, XOR shares the same traversal skeleton as join and differs only in
the algebra used to combine coincident values.