Glossary

The terms this paper uses, defined as Solieum uses them rather than in general.

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.