An equity security holder is a holder of an equity security of the debtor. Examples of an equity security are a share in a corporation, an interest of a limited partner in a limited partnership, or a right to purchase, sell, or subscribe to a share, security, or interest of a share in a corporation or an interest in a limited partnership. 11 U.S.C §§ 101(16) , (17).
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An equity security holder may vote on the plan of reorganization and may file a proof of interest, rather than a proof of claim. A proof of interest is deemed filed for any interest that appears in the debtor's schedules, unless it is scheduled as disputed, contingent, or unliquidated. 11 U.S.C. § 1111.

An equity security holder whose interest is not scheduled or scheduled as disputed, contingent, or unliquidated must file a proof of interest in order to be treated as a creditor for purposes of voting on the plan and distribution under it. Fed. R. Bankr. P. 3003(c)(2).A properly filed proof of interest supersedes any scheduling of that interest. Fed. R. Bankr. P. 3003(c)(4). Generally, most of the provisions that apply to proofs of claim, as discussed above, are also applicable to proofs of interest.