{
  "status": "shipping",
  "advantages": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-15",
  "slug": "symbol-erasure",
  "term": "Symbol erasure",
  "aliases": [
    "Known erasure"
  ],
  "definition": "A symbol erasure is a codeword position whose value is unavailable or deliberately discarded and whose location is known to the decoder.",
  "note": "An erased value is not a zero, and an incorrect value at an unidentified position remains an error. The distinction is part of the decoder input contract, not a diagnosis of why storage failed. [forney] Hesela's six-symbol example shows that identifying the actual damaged coordinate enables recovery, whereas discarding a healthy coordinate can leave a unique wrong result. [hesela-errors]",
  "limitations": [
    "A checksum mismatch only helps locate an erasure when the check and the fragment identity are trustworthy.",
    "Erasing an entire shard affects its mapped symbol positions; counts must be interpreted per codeword."
  ],
  "related": [
    "error-and-erasure-decoding",
    "reed-solomon-code",
    "erasure-coding",
    "codeword",
    "checksum"
  ],
  "citations": [
    {
      "id": "forney",
      "title": "G. David Forney. Principles of Digital Communication II, MIT 6.451 (2005), section 6.5.3: bounded-distance erasure-and-error correction.",
      "url": "https://ocw.mit.edu/courses/6-451-principles-of-digital-communication-ii-spring-2005/bb895c1dee9ce0b39d6846e0aa984981_MIT6_451S05_FullLecNotes.pdf",
      "accessed": "2026-10-15"
    },
    {
      "id": "hesela-errors",
      "title": "Hesela: exact GF(7) errors-and-erasures examples, including an ambiguous observation and false-identification negative control.",
      "url": "https://hesela.com/analyses/reed-solomon-matrix-recovery-guarantees/#errors-erasures",
      "accessed": "2026-10-15"
    }
  ]
}