> For the complete documentation index, see [llms.txt](https://solieum.gitbook.io/solieum/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://solieum.gitbook.io/solieum/glossary.md).

# Glossary

Alphabetical. Where a term has a loose industry meaning and a precise meaning here, the precise one is given.

**Admission.** The moment a transaction is accepted. On Solieum it is also the moment it is executed: a transaction that would fail is refused here, with the program's own error returned, and never enters a block.

**Air gap.** The delay between proving a withdrawal and being paid, 24 hours by the mainnet design. It exists to answer a question the challenge window cannot: whether the dispute machinery itself was sound. It is the only interval in which a key can affect a proven withdrawal, and only by denying the root it rests on.

**Batch.** The compressed bytes of one block, published on Solana. Opened with a commitment, posted in chunks, and sealed only if the bytes fold to that commitment.

**Bisection.** The dispute procedure: each round halves the disputed range of the trace, with both parties committing to the state at the midpoint, until one step remains.

**Bond.** Collateral, always in SOL. Three different ones: the **proposer bond** backs a state root, the **challenger bond** backs opening a dispute, and the **receipt bond** backs the sequencer key's ordering promises. The first two are about a root; the third is about a key.

**Challenge window.** 432,000 slots, 48 hours at Solana's 400 ms target, during which anyone may challenge a state root. It answers one question: was this root challenged.

**Compute unit.** Solana's metering unit. A transaction has 1,400,000. A witnessed one-step verification is allowed 700,000 and measures about 20,000 for a transfer.

**Data availability.** Publishing the bytes needed to rebuild the chain. If they are withheld, nobody can prove fraud and nobody can exit without permission, whatever the contracts say.

**Derivation.** Rebuilding the chain from published data alone. A rule violated, for example a forced entry skipped past its deadline, makes derivation **stop**, which invalidates everything after it while leaving everything before it standing.

**Dispute game.** The interactive protocol that turns a disagreement about a block into a disagreement about one instruction, decided by Solana.

**Fast exit.** Selling a pending withdrawal to a liquidity provider who pays now at a spread and waits out the window. A market, not a protocol guarantee, and not underwritten by anyone today.

**Forced inclusion.** Submitting a transaction directly to a Solana program, with an on-chain deadline after which the chain's derivation rules include it regardless of the operator. It promises a slot, not a successful transaction.

**Fraud proof.** The mechanism that makes an invalid state root removable. Optimistic, meaning it runs after the fact and within a window, as distinct from a validity proof.

**Guardian.** A key, 2-of-3 by the mainnet design and separate from the upgrade authority, that may pause new deposits and new roots, and deny a settlement root inside the air gap. It cannot reach a proven withdrawal's funds, redirect a payment, or change a recipient.

**Lamport.** One billionth of a SOL. Solieum's flat fee is 5,000 of them.

**One-step verifier.** The on-chain program that decides a single disputed instruction from Merkle witnesses. It cannot invoke the program being disputed, because the accounts are Layer 2 accounts that do not exist on Solana, so every instruction class it supports is re-implemented inside it and held to the real program by a differential test.

**Opaque step.** A step in the trace that no current verifier class can execute, committed under a domain no verifier knows so it can never be mistaken for a witnessable one. Deposits, withdrawals and anything through a registered program are opaque today. Each block publishes how many of its steps are opaque.

**Optimistic rollup.** A rollup where a proposed state root is assumed correct unless challenged. The assumption buys cheap execution; the challenge window is what it costs.

**Ordering receipt.** A signature the sequencer gives at admission fixing a transaction's batch and position **before** execution. Two receipts for one position, or a batch contradicting a receipt, is provable equivocation and takes the bond.

**Relay address.** The program-derived address that only the bridge portal can sign for. The node credits an inbox entry as a deposit only when that address submitted it, which is what stops anyone from forging a deposit-shaped entry.

**Retention.** How long a finalized root or a sealed batch record is kept before its rent is reclaimed. For roots it is a **proving deadline**, because closing a root ends the ability to prove new withdrawals against it.

**Rollup, validium, sidechain.** Where the data lives decides which word applies. Data on Solana is a **rollup**. Data on an external availability layer is a **validium**, with that provider as a second trust root. Data held only by the operator is neither: it is a system you trust the operator to run.

**Sequencer.** The operator that orders transactions and produces blocks. On Solieum it is a single party today, which is a liveness and ordering monopoly, made survivable by receipts, a bond, forced inclusion and deterministic replay. A future staked sequencer set would decide **ordering only**; finality stays with Solana.

**Settlement.** Committing state roots to the Solana program that holds them, and the finality rules that program enforces.

**Slot.** Solana's block interval, targeted at 400 ms and measuring about 166 ms on devnet. Solieum denominates its window and every dispute deadline in slots rather than seconds, so a halted chain cannot time an honest party out.

**Sparse Merkle tree.** The state commitment: fixed depth 256, where a key's own bits determine its leaf position. It makes insertion and deletion witnessable and non-inclusion provable, which a sorted-leaf tree cannot do in bounded work.

**State root.** A 32-byte commitment to the whole Layer 2 state after a block. What a proposer commits under bond, what a challenger disputes, and what a withdrawal is proven against.

**Step.** One state transition the node applied: a fee, one instruction of a successful transaction, a withdrawal, or a deposit credit. A consumed forced entry that changed nothing is not a step.

**SVM.** The Solana Virtual Machine. Solieum forks Agave's implementation rather than reimplementing it, so a program compiled for Solana runs unchanged.

**Trace.** What a dispute is actually about: the sequence of state commitments, one per step, with the block's pre-state at one end and its post-state at the other.

**Validity proof.** A proof that a state transition is correct, checked at commit time rather than after a waiting period. Planned as a **second** independent gate alongside fraud proofs, never as a replacement, because a soundness bug in a single prover is silent and total.

**Vault.** The account the bridge portal owns and pays withdrawals from. It pays only what it holds, and only against a proof.

**Watchtower.** A verifier running continuously: re-deriving the chain from Solana through independent readers that must agree, checking each batch, checking bridged supply against the vault, and able to open a challenge under bond. Nobody outside the operator runs one yet.

**Withdrawal leaf.** The commitment placed in the state tree when a withdrawal is initiated, and recomputed by the portal when it is proven. Leaves never expire, so a holder can prove against any retained final root.