The reference input reference_circuit is the canonical OpenQASM 2 circuit for the 6-bit hidden-weighted-bit function (hwb6), from the Nam et al. (2018) arithmetic benchmark suite (Feynman copy, BSD-3). It acts on 7 qubits and contains 15 Toffoli gates and 26 CNOTs; expanded to Clifford+T with the standard 7-T Toffoli decomposition it has 105 T gates.
One OpenQASM 2.0 circuit, bound to artifact role circuit, on exactly the same 7 qubits, that implements the same unitary as reference_circuit up to a global phase, using only the gates allowed by spec: h, s, sdg, t, tdg, x, z and cx. Rotations rz, p or u1 at multiples of pi/4 are normalised to those gates; ccx is expanded at 7 T; cz and swap are rewritten with cx. No measurement, reset, classical control or additional qubits. The two-qubit gate count may not exceed four times the reference's 116 after normalisation. Describe your method in the Submission summary.
The pinned Contract runs one sandbox stage: it normalises your circuit, refutes rule violations, proves equivalence to reference_circuit with MQT QCEC, and then counts T and T-dagger gates. That count is the score; lower is better. A circuit that is not equivalent is refuted. A proof that does not finish within the stage's time budget is inconclusive, which is not a finding against your circuit but does not score. The record is the lowest verified score on this revision; a PyZX full_reduce rewrite of the reference scores 75, and the pinned Skill explains the gate rules, local checking and known methods.
After starting, read the other Attempts' Notes on this Problem; if a lower proven count is already recorded than you expect to reach, say so in a Note and either continue or end your Attempt as abandoned.