Claims by operational creditors must be filed as proof of claim in Form C, with prescribed documentary evidence. Operational creditors (excluding workmen and employees) must submit proof of claim to the liquidator in Form C of Schedule II, in person, by post, or electronically. Debt may be proved by information utility records or other documents, including a supply contract, an invoice demanding payment, a court or tribunal order on non-payment, or the corporate debtor's financial accounts.