contract NOCUSTCommitChain is
    BimodalProxy,
    DepositProxy,
    WithdrawalProxy,
    ChallengeProxy,
    RecoveryProxy {
  using SafeMathLib256 for uint256;

  /**
   * This is the main constructor.
   * @param blocksPerEon - The number of blocks per eon.
   * @param operator - The IMMUTABLE address of the operator.
   */
  constructor(uint256 blocksPerEon, address operator)
    public
    BimodalProxy(blocksPerEon, operator)
  {
    // Support ETH by default
    ledger.trailToToken.push(address(this));
    ledger.tokenToTrail[address(this)] = 0;
  }

  /**
   * This allows the operator to register the existence of another ERC20 token
   * @param token - ERC20 token address
   */
  function registerERC20(
    ERC20 token
  )
    public
    onlyOperator()
  {
    require(ledger.tokenToTrail[token] == 0);
    ledger.tokenToTrail[token] = uint64(ledger.trailToToken.length);
    ledger.trailToToken.push(token);
  }

  /**
   * This method allows the operator to submit one checkpoint per eon that
   * synchronizes the commit-chain ledger with the parent chain.
   * @param accumulator - The accumulator of the previous eon under which this checkpoint is calculated.
   * @param merkleRoot - The checkpoint merkle root.
   */
  function submitCheckpoint(
    bytes32 accumulator,
    bytes32 merkleRoot
  )
    public
    onlyOperator()
    onlyWhenContractUnpunished()
  {
    uint256 eon = ledger.currentEon();
    require(
      ledger.parentChainAccumulator[eon.sub(1).mod(ledger.EONS_KEPT)] == accumulator,
      'b');
    require(
      ledger.getLiveChallenges(eon.sub(1)) == 0,
      'c');
    require(
      eon > ledger.lastSubmissionEon,
      'd');

    ledger.lastSubmissionEon = eon;

    BimodalLib.Checkpoint storage checkpoint = ledger.getOrCreateCheckpoint(eon, eon);
    checkpoint.merkleRoot = merkleRoot;

    emit CheckpointSubmission(eon, merkleRoot);
  }
}
/**
 * This is the main Parent-chain Verifier contract. It inherits all of the proxy
 * contracts and provides a single address to interact with all the moderated
 * balance pools. Proxies define the exposed methods, events and enforce the
 * modifiers of library methods.
 */
function registerERC20(
    ERC20 token
  )
    public
    onlyOperator()
  {
    require(ledger.tokenToTrail[token] == 0);
    ledger.tokenToTrail[token] = uint64(ledger.trailToToken.length);
    ledger.trailToToken.push(token);
  }
/**
 * This allows the operator to register the existence of another ERC20 token
 * @param token - ERC20 token address
 */