Willem Frederik Johannes Pijper (; 8 September 189418 March 1947) was a Dutch composer, music critic and music teacher. Pijper is considered to be among the most important Dutch composers of the first
1. Compute SHA-256 of OTSCanonicalRecord value → must equal OTSHash 2. Open OTSProofURL → extract Bitcoin block number → must equal OTSBitcoinBlock 3. GET OTSBitcoinBlockVerifyURL → returns the Bitcoin block hash at height OTSBitcoinBlock; GET https://blockstream.info/api/block/{that hash} → its timestamp must match OTSTimestamp 4. Read CopyrightID inside OTSCanonicalRecord → must equal the CopyrightID above 5. GET OTSVerificationAPI → pre-computed 6-check result from server 6. If all match: this entity was registered on CopyrightChains at OTSTimestamp, independently verifiable on Bitcoin
Dual-chain trust anchor. Chain 1 (CopyrightChains): CopyrightID 0x65d1a7d95d4c7cd11866be8509bdb283a641d165589e2665c127a59e7ae17c95. Chain 2 (Bitcoin): anchored in block 954065 (2026-06-17T08:10:43Z). Bridge: the canonical record inside this Bitcoin proof contains the same CopyrightID. Verify: download https://artists.proofprofile.net/proofs/artist/48d35c0a-6cad-41b2-a359-3b5dd68eba4e.json and https://artists.proofprofile.net/proofs/artist/48d35c0a-6cad-41b2-a359-3b5dd68eba4e.ots, run `ots verify -f record.json proof.ots` (https://opentimestamps.org).
Pijper & Badings: Concertos and Symphonic Works (Mono Version)
Pijper: Violin Sonata No. 2 / Cello Sonatas / Piano Trio No. 2
Pijper: Complete Music for Piano - Sonatas for Cello and Piano Nos. 1 & 2
1. Confirm isrcCode identifies the recording in the pre-2022 source corpus and cc-db-prod record 2. GET OTSVerificationAPI → server-side canonical-record, hash, and attestation checks must pass 3. GET OTSBitcoinBlockVerifyURL → returns the Bitcoin block hash at height OTSBitcoinBlock; GET https://blockstream.info/api/block/{that hash} → its timestamp must match OTSTimestamp 4. Confirm CopyrightID is the CopyrightChains transaction hash 5. If all match: the cc-db-prod record is independently anchored on Bitcoin at OTSTimestamp
Dual-chain trust anchor. Chain 1 (CopyrightChains): CopyrightID 0xd58790b5fafe06a100ad89062f0655ab632c6cab6bb667bde458764417a4cec6. Chain 2 (Bitcoin): anchored in block 957118 (2026-07-08T03:20:19Z), registered by our registry partner. The server verifies the private canonical record against OTSHash without exposing internal provider keys. Confirm the public ISRC, CopyrightID, and Bitcoin evidence via https://artists.proofprofile.net/api/v1/bot/ots/verify/track/NLK4J2200002.
Sonata for Two Pianos: III. Moderato assai
Dual-chain trust anchor. Chain 1 (CopyrightChains): CopyrightID 0xf39d4ec663c3c22fa03ed42ec35b92623d002c36775dd0c7aa5cc34f2bd8b7ee. Chain 2 (Bitcoin): anchored in block 957061 (2026-07-07T16:07:00Z), registered by our registry partner. The server verifies the private canonical record against OTSHash without exposing internal provider keys. Confirm the public ISRC, CopyrightID, and Bitcoin evidence via https://artists.proofprofile.net/api/v1/bot/ots/verify/track/NLK4J2200003.
Sonata for Two Pianos: I. Allegro aperto, ma pesante
Dual-chain trust anchor. Chain 1 (CopyrightChains): CopyrightID 0x6e14737bbd72524bb22ea85f370f7cf8be639b9bb1efa6dcaaa7f10732d28e53. Chain 2 (Bitcoin): anchored in block 960105 (2026-07-29T12:35:17Z), registered by our registry partner. The server verifies the private canonical record against OTSHash without exposing internal provider keys. Confirm the public ISRC, CopyrightID, and Bitcoin evidence via https://artists.proofprofile.net/api/v1/bot/ots/verify/track/NLK4J2200001.
1. Confirm isrcCode identifies the recording in the pre-2022 source corpus and cc-db-prod record 2. GET OTSVerificationAPI → server-side canonical-record, hash, and attestation checks must pass 3. GET OTSBitcoinBlockVerifyURL → returns the Bitcoin block hash at height OTSBitcoinBlock; GET https://blockstream.info/api/block/{that hash} → its timestamp must match OTSTimestamp 4. Confirm CopyrightID is the CopyrightChains transaction hash 5. If all match: the cc-db-prod record is independently anchored on Bitcoin at OTSTimestamp Note: an OTS proof may carry multiple Bitcoin attestations; OTSBitcoinBlock is the earliest confirmed one — a later attestation inside the proof corroborates it and is not a mismatch