Encoded fan-in-two circuits

This module exposes the machine-facing representation of Basis.andOr2 circuits and its correctness theorems.

Main definitions

• CircuitCode.RawGate and RawCircuit: proof-free ordered syntax.
• RawCircuit.WellFormed: nonempty, strictly backward-pointing gate lists.
• RawCircuit.encode / decode?: canonical terminated-unary bit codec.
• RawCircuit.eval?: array-backed iterative evaluation.
• CircuitCode.encodeCircuit: serialization of a typed circuit.
• CircuitCode.evalCode: decode and evaluate with an exact arity check.

Main results

• RawCircuit.decode?_eq_some_iff: exact decoder soundness and completeness.
• RawCircuit.eval?_isSome_iff: executable success exactly matches well-formedness.
• CircuitCode.evalCode_encodeCircuit: encoded evaluation agrees with Circuit.eval.
• CircuitCode.evalCode_encodeCircuit_of_length: the corresponding list-native theorem for machine-facing clients.
• CircuitCode.encodeCircuit_length_le_size: concrete polynomial bit-length bound for the unary encoding.

theorem Complexity.CircuitCode.RawCircuit.decode?_eq_some_iff (bits : List Bool) (circuit : RawCircuit) : decode? bits = some circuit ↔ bits = circuit.encode

Exact decoding succeeds precisely on canonical raw-circuit encodings.

theorem Complexity.CircuitCode.RawCircuit.eval?_isSome_iff (circuit : RawCircuit) (input : List Bool) : (circuit.eval? input).isSome = true ↔ WellFormed input.length circuit

Raw evaluation succeeds precisely for nonempty topologically ordered circuits at the supplied input arity.

theorem Complexity.CircuitCode.evalCode_encodeCircuit {N G : ℕ} [NeZero N] (c : Circuit Basis.andOr2 N 1 G) (input : BitString N) : evalCode N (encodeCircuit c) input.toList = some (c.eval input 0)

Decoding and iteratively evaluating the canonical encoding of a typed fan-in-two circuit returns its typed output.

theorem Complexity.CircuitCode.evalCode_encodeCircuit_of_length {N G : ℕ} [NeZero N] (c : Circuit Basis.andOr2 N 1 G) (input : List Bool) (hinput : input.length = N) : evalCode N (encodeCircuit c) input = some (c.eval (BitString.ofList input hinput) 0)

List-native semantic correctness for an input of the declared arity.

theorem Complexity.CircuitCode.encodeCircuit_length_le_size {N G : ℕ} [NeZero N] (c : Circuit Basis.andOr2 N 1 G) : (encodeCircuit c).length ≤ 1 + c.size * (2 * (N + c.size) + 6)

In the library's size convention, which counts internal and output gates but not primary inputs or free negations, unary circuit codes have quadratic length in the input arity and circuit size.