let insuranceToken = base58'8jfD2JBLe23XtCCSQoTx5eAW5QCU6Mbxi3r78aNQLcNf'
#extracting the sender’s address from the transaction
let this = extract(tx.sender)
let freezePeriod = 150000
let insurancePrice = 10000
match tx {
  #verifying that if a DataTransaction has arrived, it has just one field and there is no second key in the state
  case d : DataTransaction => size(d.data) == 1 && !isDefined(getBinary(this, d.data[0].key))
  case e : ExchangeTransaction =>
    #if a transaction doesn’t have the seventh proof, we’re verifying the signature
    if !isDefined(e.proofs[7]) then
       sigVerify(e.bodyBytes, e.proofs[0], e.senderPublicKey)
       else
        #if the transaction has the seventh proof, we’re extracting from it the transaction and discovering its height
        let purchaseTx = transactionById(e.proofs[7])
        let purchaseTxHeight = extract(transactionHeightById(e.proofs[7]))
        #processing the transaction from the proof
        match purchaseTx {
          case purchase : ExchangeTransaction =>
          let correctSender = purchase.sender == e.sellOrder.sender
          let correctAssetPair = e.sellOrder.assetPair.amountAsset == insuranceToken &&
          purchase.sellOrder.assetPair.amountAsset == insuranceToken &&
          e.sellOrder.assetPair.priceAsset == purchase.sellOrder.assetPair.priceAsset
          let correctPrice = e.price == purchase.price - insurancePrice && e.amount == purchase.amount
          let correctHeight = height > purchaseTxHeight + freezePeriod
          #verifying that the current transaction’s ID is stated correctly in the proof transaction
          let correctProof = extract(getBinary(this, toBase58String(purchase.id))) == e.sellOrder.id
          correctSender && correctAssetPair && correctPrice && correctHeight && correctProof
          case _ => false
        }
  case _ => sigVerify(tx.bodyBytes, tx.proofs[0], tx.senderPublicKey)
}