{
  "title": "Bitcoin: the currency of the future? · In progress",
  "introTitle": "Claims and initial research",
  "scope": "Digital adaptation of the learner activities on pages 1–29 of Till Favier’s Blockchain workbook. The original ZIP remains available. This version stays work in progress until content equivalence, including the supplementary hints and pedagogical changes, has been reviewed. Simplifications and historical assumptions are identified in the relevant chapters.",
  "videoTask": "Watch the source’s introductory video [ALL IN #bitcoin! Aus Überzeugung](https://www.youtube.com/watch?v=R6gmTuI1Yp0). Summarize its central claim.",
  "videoOpinion": "Does the video initially convince you? Explain why or why not.",
  "claimsTask": "Research the three claims. Explain their supposed advantage and record how plausible each initially seems, including a source or reason. Add at least one claim of your own. These are claims to investigate, not established facts. The final reassessment is saved in a separate table in the last chapter; your initial answers remain here.",
  "claimsTitle": "Claims about Bitcoin",
  "claim1": "Claim 1",
  "claim2": "Claim 2",
  "claim3": "Claim 3",
  "own1": "Own claim 1",
  "own2": "Own claim 2",
  "claim": "Claim",
  "explanation": "Explanation / source",
  "assessment": "Initial plausibility",
  "anonymous": "Bitcoin is anonymous.",
  "fast": "Bitcoin is fast.",
  "decentralized": "Bitcoin is decentralized.",
  "hashTitle": "Square-middle hashing",
  "hashExplanation": "Worksheet Hashq: square an integer greater than 3, then take two middle decimal digits. If the square has an odd number of digits, take the middle digit and its left neighbor, in their original order. Examples: 57² = 3[24]9 → 24; 23² = [52]9 → 52. Keep leading zeros in the two-digit hash. This is a teaching example, not a cryptographic hash or Bitcoin’s SHA-256.",
  "boundaryTask": "Exercise 4.1: Why should the input be greater than 3?",
  "exploreTitle": "Explore Hashq",
  "exploreTask": "Compare two inputs. The highlighted digits of each square form its hash.",
  "hashTableTask": "Exercise 4.2: calculate the squares and hashes of 42, 99 and 13. Enter the square in decimal and the hash as exactly two digits.",
  "hashTableTitle": "Calculate the source examples",
  "number42": "42",
  "number99": "99",
  "number13": "13",
  "collisionTitle": "Find a collision",
  "collisionTask": "Exercise 4.3: find two different integers with the same Hashq value. Several answers work. Different spellings of the same integer do not count.",
  "preimage22Title": "Find an input for hash 22",
  "preimage77Title": "Find an input for hash 77",
  "preimageTask": "Exercise 4.4: find an input whose Hashq value is {target}. Any input that satisfies the rule is accepted.",
  "hashReflection": "Describe how you found a collision and the target inputs. Why does this simple method not provide the guarantees of a cryptographic hash?",
  "firstInput": "First input",
  "secondInput": "Second input",
  "reset": "Reset inputs",
  "calculation": "Exact decimal calculation",
  "input": "Input",
  "square": "Square",
  "hash": "Hashq",
  "invalid": "Enter a positive integer greater than 3, using at most 100 decimal digits.",
  "explorationSaved": "Inputs saved. Exploration has no automatic grade.",
  "correct": "Correct.",
  "tryAgain": "The valid inputs do not yet meet this task’s criterion.",
  "trustTitle": "Whom do I have to trust?",
  "photoStorage": "1.1: Where are your smartphone photos stored? Distinguish local storage, cloud storage and backups. You need not share personal photos or account details.",
  "cloudFailure": "1.2a: Imagine your photo-cloud provider went bankrupt and switched off its servers tomorrow. What could happen to your photos? How would local copies change the outcome?",
  "cloudLikelihood": "1.2b: How realistic is this scenario for your chosen provider? Give reasons and distinguish likelihood from the consequences.",
  "cloudTrust": "1.3: Choose a cloud provider. What exactly do you trust it to do, and what benefits do you receive in return?",
  "paymentRoute": "1.4: Describe a recent cashless payment without giving private account details. Replace the source flowchart with a sequence: sender → provider/institution → … → recipient. Name the payment method and intermediaries.",
  "paymentComparisonTask": "1.5: Compare a cash payment with making the same payment online or by bank transfer. Record advantages and disadvantages for each.",
  "paymentComparisonTitle": "Cash and online payments",
  "cash": "Cash",
  "onlinePayment": "Online payment / transfer",
  "advantages": "Advantages",
  "disadvantages": "Disadvantages",
  "thirdPartyTask": "A third party participates in a payment without being the sender or recipient (for example a bank or payment provider). Bitcoin aims to enable payments without a central trusted intermediary. Explain this motivation using Tom’s online book purchase: which roles might PayPal, Tom’s bank and the shop’s bank play?",
  "paymentArgumentsTask": "Final task 1: For each aspect, explain an advantage or disadvantage of using a third party. Buyer protection is the source’s example of an advantage. Consider whose perspective matters; reasoned answers are not automatically graded.",
  "paymentArgumentsTitle": "Arguments about third parties",
  "buyerProtection": "Buyer protection",
  "privacy": "Privacy",
  "singleFailure": "Single point of failure",
  "terms": "Terms and conditions",
  "forgottenPin": "Forgotten PIN",
  "effect": "Advantage / disadvantage / depends",
  "reason": "Reason",
  "ledgerTitle": "Keeping a ledger",
  "ledgerHistory": "Four friends use cabin points (HP) to pay for chores. Their ledger hangs above the fireplace. Entry 00 gives Anna, Lukas, Sara and Tom 10 HP each. All transfers below are in order. This is integer-point bookkeeping, not a real wallet or payment system.\n\n| Entry | From | To | HP |\n| --- | --- | --- | --- |\n| 01 | Anna | Lukas | 4 |\n| 02 | Lukas | Sara | 6 |\n| 03 | Sara | Tom | 2 |\n| 04 | Anna | Tom | 5 |\n| 05 | Anna | Sara | 1 |\n| 06 | Tom | Lukas | 12 |",
  "balanceTask": "2.1: Calculate the balances after entry 06. The PDF asks for Anna and Tom; also calculate Lukas and Sara to check that the total remains 40 HP. Enter whole numbers.",
  "balanceTitle": "Balances after entry 06",
  "balance": "Balance (HP)",
  "personAnna": "Anna",
  "personLukas": "Lukas",
  "personSara": "Sara",
  "personTom": "Tom",
  "derivedBalances": "2.2: Why need the friends not record balances separately? Explain how the history determines them.",
  "overspendTask": "2.3: After entry 06, Anna wants to pay Tom 4 HP for doing the dishes. Can this transfer be accepted without creating points or allowing debt?",
  "transferYes": "Yes",
  "transferNo": "No",
  "overspendReason": "2.3: Explain your decision using Anna’s available balance. What would need to happen first for her to pay 4 HP?",
  "ledgerFraud": "2.4: The physical ledger is accessible to everyone. What fraud or manipulation is possible? Describe an example and how someone might detect it.",
  "signedLedger": "2.5: Now every transfer must be signed by its sender. Assume signatures cannot be forged. Which attacks are prevented, and which remain possible (for example removing history)? This assumption belongs to the exercise; no signatures are generated here.",
  "storageTask": "2.6: Compare both signed-ledger proposals. Tom keeps the only ledger in his room and alone records transfers; alternatively everyone keeps an equal copy and every transfer is announced to all four. Discuss advantages and disadvantages, including conflicting copies.",
  "storageTitle": "Central or distributed storage?",
  "centralLedger": "Tom keeps the only ledger",
  "distributedLedger": "Everyone keeps a copy",
  "ledgerTrust": "2.7: Connect centralized and decentralized bookkeeping to trust from section 1. Whom must participants trust in each proposal, and about what?",
  "decentralizedReassessment": "2.8: Revisit your initial decentralization claim. Record your current assessment and reasons here; later chapters may change it again.",
  "bitcoinLedgerTask": "Final task 2: Research Bitcoin’s counterparts to handwritten sender signatures and physical ledger storage. Explain each briefly and cite a source. The cabin exercise is an analogy, not a specification of Bitcoin.",
  "bitcoinLedgerTitle": "From cabin points to Bitcoin",
  "signing": "Signing: handwritten sender signature",
  "storing": "Storage: one physical book or four copies",
  "bitcoinExplanation": "Bitcoin counterpart / explanation / source",
  "privacyTitle": "Pseudonyms and privacy",
  "pseudonymHistory": "The friends now admit more participants and use pseudonyms so that Sven cannot immediately tell who did what. The history remains public. Entry 00 gives Cookie Monster, Elmo, Oscar and Bert 10 HP each.\n\n| Entry | From | To | HP |\n| --- | --- | --- | --- |\n| 01 | Cookie Monster | Elmo | 4 |\n| 02 | Elmo | Oscar | 6 |\n| 03 | Oscar | Bert | 2 |\n| 04 | Cookie Monster | Bert | 5 |\n| 05 | Cookie Monster | Oscar | 1 |\n| 06 | Bert | Elmo | 12 |",
  "pseudonymOpinion": "3.1: How useful are pseudonyms in this public ledger? What do they conceal, and what can observers still learn?",
  "timonEntry": "3.2: Tom’s friend Timon wants his first 2 HP and offers €2. No new points may be created. Choose a pseudonym for Timon and describe a concrete exchange: whom he talks to, how payment takes place, and the ledger entry (sender pseudonym → recipient pseudonym, amount). Several valid proposals are possible.",
  "identityLeak": "3.3: How could Timon’s entry reveal the identity behind an existing pseudonym? Explain who learns what through the exchange.",
  "bitcoinPrivacyTask": "3.4: Research the Bitcoin counterparts to pseudonyms and acquiring the first points. For acquisition, consider registration and payment records. Distinguish addresses from digital signatures; an address is not itself a signature. Cite your sources.",
  "bitcoinPrivacyTitle": "Pseudonymity in Bitcoin",
  "pseudonyms": "Cabin ledger: names replaced by pseudonyms",
  "acquiring": "Cabin points: acquire existing points from a participant",
  "bitcoinIdentity": "3.5: After acquiring Bitcoin, who might link your identity to an address and subsequent public transactions? Consider exchange registration, payment records and information you disclose.",
  "bankPrivacy": "3.6: Compare this with a bank transfer. Who can see transaction details in each system? Distinguish privacy from the public and privacy from service providers.",
  "anonymousReassessment": "Final task 3: Revisit your initial anonymity claim. Record your current assessment, evidence and remaining questions here.",
  "shaTitle": "Cryptographic hashing with SHA-256",
  "shaExplanation": "SHA-256 is a cryptographic hash function in the SHA-2 family. It hashes a sequence of bytes to exactly 256 bits, displayed here as 64 hexadecimal digits. Bitcoin uses SHA-256; these text experiments are not Bitcoin block hashes. The built-in tool replaces the source’s external tool. It hashes the exact UTF-8 text, including whitespace and capitalization, without trimming or normalization. Even empty text has a hash. Inputs are limited to 4096 characters for this exercise. A cryptographic hash is designed to make finding a full-hash preimage computationally infeasible; this is not mathematical impossibility. Matching a short prefix is much easier.",
  "shaCompareTitle": "4.5: Compare SHA-256 hashes",
  "shaCompareTask": "Compare the source examples “Informatik” and “informatik”, then try your own texts. Change one character, add a space or compare identical inputs. The count measures changed bits, not changed hexadecimal digits.",
  "shaResults": "SHA-256 · 64 hexadecimal digits · 256 bits",
  "shaDifference": "{count} of 256 output bits differ. Small input changes typically change many bits; the exact count varies.",
  "shaComparisonSaved": "Texts saved. This experiment has no automatic grade.",
  "shaTextEncoding": "4.5a: Why can SHA-256 accept text as well as numbers? Explain how a text encoding turns characters into bytes. Here a typed number is hashed as its text representation.",
  "shaHexadecimal": "4.5b: Why does the output mix digits and letters a–f? How many bits does one hexadecimal digit represent?",
  "shaAvalanche": "4.5c: Describe your observations for similar inputs. Are identical inputs different? Does every one-character change flip exactly half the output bits? Explain using examples.",
  "shaSpaceTask": "4.6: How many different 256-bit output values are possible? Enter a power using ^, or the exact decimal number.",
  "shaSpaceTitle": "Size of the hash space",
  "sha256Bits": "256 bits",
  "shaPossibleOutputs": "Number of possible values",
  "shaPrefixOneTitle": "Final task 4: Find a hash beginning with zero",
  "shaPrefixTwoTitle": "Optional extension: Find two leading zeros",
  "shaPrefixTask": "Try input texts until the hash starts with at least {zeros} hexadecimal zero(s). Every matching input is accepted. Change the text yourself; no automatic search runs.",
  "shaTryAgain": "The hash does not yet have the required zero prefix. Try another input.",
  "shaDifficultyReflection": "Final task 4: How much longer would you expect to need for two leading hexadecimal zeros instead of one, and why? Explain why searching a short prefix does not mean you can efficiently invert an entire 256-bit hash.",
  "shaDifficultyHintTitle": "Hint: Expected number of attempts",
  "shaDifficultyHint": "Each hexadecimal digit has 16 possibilities. For independent uniformly distributed trials, expect about 16 attempts for one leading zero and 256 for two (16 times as many). This is an average, not a guaranteed waiting time. A full 256-bit preimage search has a vastly larger target space.",
  "powTitle": "Linked blocks and proof of work",
  "powConflictingCopies": "5.1a: Anna deletes her outgoing transfers from her private copy and claims to have 10 HP. Tom’s copy gives her 0 HP. Describe the problem when she offers him 4 HP for doing the dishes.",
  "powOtherConflict": "5.1b: Describe another situation in which participants’ ledger copies could disagree.",
  "powProposals": "5.2: Propose a way to resolve conflicting copies without appointing one central ledger keeper. What assumptions does your proposal require?",
  "powExplanation": "The source splits issuance and six transfers into four blocks, with at most two records per block. Each hash covers its position, predecessor hash, nonce and exact UTF-8 data. Changing an early block therefore changes later hashes. Open the editor, mine blocks from first to last, edit an early record and observe the consequences. The quick lab requires one leading hexadecimal zero; the separate four-zero lab matches the source’s difficulty. Initial record text uses the original German pseudonyms in both languages, so changing the display language never changes the chain. This teaching format uses single SHA-256, not Bitcoin’s binary block headers or double hashing. A valid proof does not verify balances, signatures or consensus.",
  "powSimulatorTitle": "Quick block-chain lab",
  "powBlockCapacity": "5.3: Research roughly how many transactions fit into a Bitcoin block. Explain why this is not a fixed transaction count and cite a source.",
  "powGenesis": "5.4: Why is the first block’s predecessor hash all zeros in this teaching chain?",
  "powReadOnlyFields": "5.5a: Why are only the data and nonce editable, while predecessor and hash are derived read-only fields?",
  "powPropagation": "5.5b: Change data or a nonce. Which hashes change and which earlier blocks stay unchanged? Explain the dependency.",
  "powColors": "5.5c: Explain the border colors and status text. Distinguish a block’s own zero-prefix proof from a valid prefix of the whole chain. A later mined block still depends on its predecessors.",
  "powMining": "5.5d: The first seven cabin ledger records are already loaded. Press Mine and describe what changes, what stays fixed and why the search may need many attempts.",
  "powPrefixConnection": "5.6: How does mining relate to finding a hash with leading zeros in the previous chapter?",
  "powTamper": "5.7a: First mine all four blocks in the quick lab, then change a transaction in the first block. What happens to subsequent hashes and proof status?",
  "powRepair": "5.7b: What must you do to obtain a fully mined chain again? Explain why remaking an early block can undo work already done on later blocks.",
  "powExpectedTask": "5.7c / 5.8: Calculate the expected attempts for four leading hexadecimal zeros. If each of four people can try 40,000 nonces per day, how many blocks can the group mine per day on average? Use the exact probability, allowing fractional averages. Enter a decimal number or the exact fraction for the second answer.",
  "powExpectedTitle": "Expected work at source difficulty",
  "powFourZeroAttempts": "Attempts per block: four hex zeros",
  "powGroupPages": "Group blocks per day: 4 × 40,000 attempts",
  "powExpectedValue": "Expected value",
  "powExpectedHintTitle": "Hint: Four hexadecimal zeros",
  "powExpectedHint": "Each hex digit has 16 possible values. Four specified zeros have probability 1/16^4, giving 65,536 attempts per block on average. Divide the group’s 160,000 daily attempts by that number. The source rounds the attempt count to about 65,000; this exercise uses the exact value.",
  "powFourZerosTask": "Optional performance experiment: this lab requires the original four leading zeros. Each Mine action stops after at most 5,000 trials, yielding between batches; repeat it if the budget is exhausted. Stop, reset, editing or closing cancels the current search. Completing this slower lab is not required to answer the reflections.",
  "powFourZerosTitle": "Original-difficulty lab: four zeros",
  "powAverage": "5.9: Why can mining throughput only be described as an average, rather than a promised completion time?",
  "powLongest": "5.10: The cabin group proposes choosing the longest valid chain. Why can someone not simply create many arbitrary blocks? This simplification assumes equal difficulty; Bitcoin compares cumulative proof of work among valid chains, not just block count.",
  "powRewrite": "5.11: Explain why Anna must redo later work after changing old transfers. Why does this make rewriting expensive without making it mathematically impossible?",
  "powAttackGuess": "Final task 5a: Make a hypothesis about what a 51% attack means and which assumptions it threatens.",
  "powAttackResearch": "Final task 5b: Research and check your hypothesis. Describe what a majority-hashpower attacker can and cannot do; distinguish rewriting recent history or double spending from forging other people’s signatures. Cite a source.",
  "blockEditorTitle": "Block-chain editor",
  "blockEditorExplanation": "Required prefix: {zeros} hexadecimal zero(s). Edit data or integer nonces (0–2147483647); predecessor and full hash are derived. Mine from first to last. Mining tries at most 5,000 candidates per action in small batches. Block text is limited to 4096 characters. Status describes proof of work only, not transaction validity.",
  "blockNumber": "Block #{index}",
  "blockData": "Data",
  "blockNonce": "Nonce",
  "blockPrevious": "Predecessor hash (derived)",
  "blockHash": "Block hash (derived)",
  "blockNonceInvalid": "Enter an integer from 0 to 2147483647. This draft has not changed the saved nonce.",
  "blockValid": "Proof meets the prefix rule; all predecessors do too.",
  "blockBlocked": "Own proof meets the rule, but an earlier block does not.",
  "blockInvalid": "Own hash does not meet the prefix rule.",
  "blockMine": "Mine this block",
  "blockReset": "Reset chain",
  "blockStop": "Stop mining",
  "blockProgress": "{count} of {total} blocks form a valid mined prefix · {zeros} leading hex zero(s)",
  "miningIdle": "No search is running.",
  "miningRunning": "Mining… {attempts} attempts in this run.",
  "miningFound": "Matching nonce found after {attempts} attempts in this run.",
  "miningStopped": "Search stopped after {attempts} attempts.",
  "miningChanged": "Chain changed; the old search was cancelled.",
  "miningBudget": "Attempt budget reached ({attempts}). Mine again to continue searching.",
  "miningExhausted": "Nonce range exhausted after {attempts} attempts. Change the block data or reset the nonce.",
  "energyTitle": "Mining, rewards and resource costs",
  "energyExplorerTask": "6.1 / 6.2a: Use the source’s [Bitcoin block explorer](https://btcscan.org/blocks/recent), or another explorer you can cite. Record the latest block and genesis block: height, leading hexadecimal zeros, coinbase reward, notable transactions and source/retrieval date. These live research answers are not automatically graded. Distinguish the coinbase transaction (protocol term) from the exchange of the same name, and subsidy from transaction fees.",
  "energyResearchTitle": "Research actual Bitcoin blocks",
  "energyLatest": "Latest block at retrieval time",
  "energyGenesis": "Genesis block",
  "energyHeight": "Block height",
  "energyHashZeros": "Leading hex zeros",
  "energyReward": "Coinbase reward / subsidy / fees",
  "energyTransactions": "Transactions / observations",
  "energySourceDate": "Source and retrieval date",
  "energyRewardChange": "6.2b: Why does the latest subsidy differ from the genesis subsidy? Research the halving rule and explain what determines future subsidies.",
  "energyFees": "6.2c: The source uses 3.125 BTC as its subsidy example. Check the subsidy appropriate to your chosen block height. Why can the coinbase transaction’s total differ from the scheduled subsidy?",
  "energyIncentive": "6.3: Explain why a reward provides an incentive to mine and how it relates to hardware, electricity costs and transaction fees.",
  "energyHistoricalTask": "6.4: The source reports 173 TWh electricity, 86 megatonnes CO₂ and 1.65 km³ water for 2020–2021. Treat these as historical source quantities, not independently verified current measurements. Convert the units below, then research and justify everyday comparisons. Enter conversion values without thousands separators. For the later difficulty questions: Bitcoin adjusts a numeric target, normally every 2016 blocks, toward a ten-minute average; a count of leading zeros is only a rough visual indication.",
  "energyConversionTitle": "Convert the source quantities",
  "energyTwh": "173 TWh → kWh",
  "energyMegatonnes": "86 Mt CO₂ → kg CO₂",
  "energyWaterVolume": "1.65 km³ water → litres",
  "energyConverted": "Value in the target unit",
  "energyElectricityComparison": "6.4a: Find a comparison for 173 TWh (the source suggests about 0.1 kWh per hour of television). Show the conversion, assumptions and a source.",
  "energyCarbonComparison": "6.4b: Find and explain a comparison for 86 megatonnes CO₂. State the period and boundary of your comparison.",
  "energyWaterComparison": "6.4c: Find and explain a comparison for 1.65 km³ water. Distinguish consumption from withdrawal if your source does.",
  "energyDifficultyOld": "6.5a: What would happen to block timing if mining power increased but the difficulty stayed at the genesis level?",
  "energyPopularity": "6.5b: If popularity attracted more mining power, how would the target/difficulty respond? Explain why popularity alone does not directly set difficulty.",
  "energyCostEffect": "6.5c: What could changing mining power imply for energy costs? Consider hardware efficiency and economic incentives rather than assuming a fixed energy cost per hash.",
  "energyArithmeticTask": "6.6a / 6.8a: For this classroom estimate only, assume 4000 transactions per block, one block every 600 seconds, 365 days and 173 TWh per year. The source earlier gives 173 TWh for 2020–2021 but later calls it annual; that period inconsistency is not a factual annual estimate here. Calculate annual blocks, annual transactions, transactions per second and allocated kWh per transaction. Counts are whole numbers; round the last two rows to two decimal places. This allocation divides assumed network energy by transactions; it is not the marginal energy caused by adding one payment.",
  "energyArithmeticTitle": "Explicit classroom throughput and energy estimate",
  "energyBlocksYear": "Blocks per 365-day year",
  "energyTransactionsYear": "Transactions per year",
  "energyTransactionsSecond": "Transactions per second (two decimals)",
  "energyAllocation": "Allocated kWh per transaction (two decimals)",
  "energyValue": "Calculated value",
  "energyThroughputProblem": "6.6b: Explain possible problems of limited base-layer throughput. The source compares its estimate with a claimed VISA capacity of 65,000 transactions/second; verify the source and distinguish maximum capacity from observed traffic and confirmation/finality.",
  "energySpeedReassessment": "6.7: Revisit your initial speed claim. Record evidence about throughput, latency and settlement instead of treating them as the same measure.",
  "energyEverydayComparison": "6.8b: Compare the allocated kWh value with an everyday activity. Show units, assumptions and the limitations of the comparison.",
  "energyPaymentResearch": "6.8c: Research energy or electricity costs of a conventional online payment (for example VISA or PayPal). Cite the date, units and system boundaries; explain whether the estimates are comparable.",
  "conclusionTitle": "Reassess the claims and form a judgment",
  "finalClaimsTask": "Final task 6: Return to your initial research and the intermediate reassessments. Complete the final table for the three source claims and your own claims, explaining evidence and changes of opinion. This separate table preserves your original answers. If you added only one own claim, you may record “not used” for the second row. These judgments are not automatically graded.",
  "finalClaimsTitle": "Final assessment of the initial claims",
  "finalAssessment": "Final assessment",
  "finalEvidence": "Evidence / reasoning / changed view",
  "energyFinalJudgment": "Final task 6: How justified do you consider Bitcoin’s resource costs after studying the workbook? Refer to the advantages and disadvantages in your claim table, distinguish facts from value judgments, and acknowledge uncertainty and counterarguments.",
  "outlook": "You have investigated trust, bookkeeping, pseudonymity, hashing, proof of work and resource costs. Bitcoin is one example of blockchain technology; other systems may use different consensus mechanisms, data models and applications (including NFTs). Do not assume that every blockchain inherits Bitcoin’s mining or energy characteristics. The digital adaptation remains in progress pending content-equivalence review; the classic workbook and supplementary materials remain available."
}