src/osec.py

"""Order-Selective Erasure Calculus (OSEC), finite reference implementation.

Only integer bit masks and exact Boolean operations are used.  An action never
creates a token.  The universal/permutation theorems concern distinct-action
words; this implementation rejects repeated actions in its protocol runner.
The erasers themselves are defined on every subset, including off-protocol ones.
"""
from __future__ import annotations
from dataclasses import dataclass
from itertools import combinations, permutations
from typing import Iterable, Iterator, Sequence


def sign(word: Sequence[int]) -> int:
    """Sign of the relative ordering of distinct, comparable labels."""
    if len(set(word)) != len(word):
        raise ValueError("Permutation labels must be distinct.")
    return -1 if sum(a > b for k, a in enumerate(word) for b in word[k+1:]) % 2 else 1


def parity_combine(left: tuple[bool, bool], right: tuple[bool, bool]) -> tuple[bool, bool]:
    """Dual-rail XOR using AND/OR only. Rails mean 'even/odd is possible'."""
    e, o = left
    f, p = right
    return (e and f) or (o and p), (e and p) or (o and f)


def parity_reduce(rails: Sequence[tuple[bool, bool]]) -> tuple[bool, bool]:
    """Balanced Boolean circuit; 6(q-1) binary gates for q >= 1 pairs."""
    if not rails:
        return True, False
    level = list(rails)
    while len(level) > 1:
        nxt = [parity_combine(level[j], level[j+1]) for j in range(0, len(level)-1, 2)]
        if len(level) % 2:
            nxt.append(level[-1])
        level = nxt
    return level[0]


@dataclass(frozen=True)
class ErasureSystem:
    """m independent n-label blocks. Each block has n markers and n(n-1) rails."""
    n: int = 3
    blocks: int = 1

    def __post_init__(self) -> None:
        if not isinstance(self.n, int) or isinstance(self.n, bool) or self.n < 2:
            raise ValueError("n must be an integer >= 2.")
        if not isinstance(self.blocks, int) or isinstance(self.blocks, bool) or self.blocks < 1:
            raise ValueError("blocks must be an integer >= 1.")

    @property
    def cells(self) -> int:
        return self.blocks * self.n * self.n

    @property
    def action_count(self) -> int:
        return self.blocks * self.n

    @property
    def pair_count(self) -> int:
        return self.blocks * self.n * (self.n-1) // 2

    @property
    def full(self) -> int:
        return (1 << self.cells) - 1

    @property
    def actions(self) -> tuple[tuple[int, int], ...]:
        return tuple((b, i) for b in range(self.blocks) for i in range(self.n))

    def _check_label(self, b: int, i: int) -> None:
        if not 0 <= b < self.blocks or not 0 <= i < self.n:
            raise ValueError("Invalid block or action label.")

    def marker(self, b: int, i: int) -> int:
        self._check_label(b, i)
        return 1 << (b*self.n*self.n + i)

    def rail(self, b: int, i: int, j: int) -> int:
        self._check_label(b, i)
        self._check_label(b, j)
        if i == j:
            raise ValueError("An order rail needs two different labels.")
        j_index = j if j < i else j-1
        return 1 << (b*self.n*self.n + self.n + i*(self.n-1) + j_index)

    def erase(self, state: int, action: tuple[int, int]) -> int:
        """E_i(S) removes c_i and r_ij for each absent marker c_j.

        Guards are evaluated on the input state. All removals are simultaneous.
        """
        if not isinstance(state, int) or isinstance(state, bool) or state < 0 or state & ~self.full:
            raise ValueError("State is not a valid subset of this universe.")
        b, i = action
        self._check_label(b, i)
        kill = self.marker(b, i)
        for j in range(self.n):
            if j != i and not state & self.marker(b, j):
                kill |= self.rail(b, i, j)
        return state & ~kill

    @staticmethod
    def flush(state: int) -> int:
        """A common terminal eraser. No log or observer memory is preserved."""
        return 0

    def run(self, word: Sequence[tuple[int, int]], *, flush: bool = False) -> list[int]:
        if len(set(word)) != len(word):
            raise ValueError("The certified protocol uses each action at most once.")
        trace = [self.full]
        for action in word:
            trace.append(self.erase(trace[-1], action))
        if flush:
            trace.append(0)
        return trace

    def parity_rails(self, state: int) -> tuple[bool, bool]:
        return parity_reduce([
            (bool(state & self.rail(b, i, j)), bool(state & self.rail(b, j, i)))
            for b in range(self.blocks) for i in range(self.n) for j in range(i+1, self.n)
        ])

    def observe(self, state: int, orientation: int = 1) -> bool:
        if orientation not in (-1, 1):
            raise ValueError("orientation is +1 or -1.")
        return self.parity_rails(state)[0 if orientation == 1 else 1]

    def extinction(self, word: Sequence[tuple[int, int]], orientation: int = 1) -> int | None:
        """First false readout, with a common flush appended (time zero included)."""
        for k, state in enumerate(self.run(word, flush=True)):
            if not self.observe(state, orientation):
                return k
        return None

    def induced_sign(self, word: Sequence[tuple[int, int]]) -> int:
        if len(set(word)) != len(word):
            raise ValueError("Repeated actions are outside the certified protocol.")
        product = 1
        for b in range(self.blocks):
            product *= sign([i for block, i in word if block == b])
        return product

    def saturated(self, local_orders: Sequence[Sequence[int]]) -> int:
        if len(local_orders) != self.blocks:
            raise ValueError("One local ordering is required per block.")
        state = 0
        for b, order in enumerate(local_orders):
            if sorted(order) != list(range(self.n)):
                raise ValueError("A local ordering must be a permutation of range(n).")
            for k, i in enumerate(order):
                for j in order[k+1:]:
                    state |= self.rail(b, i, j)
        return state

    def chain_certificate(self, local_orders: Sequence[Sequence[int]]) -> int:
        if len(local_orders) != self.blocks:
            raise ValueError("One local ordering is required per block.")
        state = 0
        for b, order in enumerate(local_orders):
            if sorted(order) != list(range(self.n)):
                raise ValueError("Invalid local permutation.")
            for i, j in zip(order, order[1:]):
                state |= self.rail(b, i, j)
        return state

    def describe(self, state: int) -> list[str]:
        tokens = []
        for b in range(self.blocks):
            for i in range(self.n):
                if state & self.marker(b, i):
                    tokens.append(f"c[{b},{i}]")
            for i in range(self.n):
                for j in range(self.n):
                    if i != j and state & self.rail(b, i, j):
                        tokens.append(f"r[{b},{i}<{j}]")
        return tokens


def all_distinct_words(actions: Sequence[tuple[int, int]]) -> Iterator[tuple[tuple[int, int], ...]]:
    for k in range(len(actions)+1):
        yield from permutations(actions, k)


def is_subsequence(word: Sequence[int], order: Sequence[int]) -> bool:
    it = iter(order)
    return all(any(x == y for y in it) for x in word)


def dnf_value(state: int, terms: Iterable[int]) -> bool:
    return any(state & term == term for term in terms)