# Assertion

**Last Updated:** 2025-01-31
**Confidence:** High

## Summary

The Assertion is the atomic unit of Episteme. It represents a signed claim about reality, not a mutable fact.

**Key Facts:**
- Immutable once written (append-only)
- Content-addressed by BLAKE3 hash
- Contains: subject, predicate, object, source, agent, timestamp
- Optionally includes vector embedding for semantic search

**File Pointer:** `crates/stemedb-core/src/assertion.rs` (planned)

## Structure

```rust
pub struct Assertion {
    pub subject: EntityId,      // "Tesla_Inc"
    pub predicate: RelationId,  // "has_revenue"
    pub object: ObjectValue,    // Float(96.7B), String("Musk"), Ref(EntityId)
    pub source: SourceHash,     // Evidence pointer (PDF/URL hash)
    pub agent: AgentId,         // Ed25519 public key
    pub timestamp: u64,         // Wall clock time
    pub vector: Option<Vec<f32>>, // Semantic embedding
}
```

## Identity

Assertion ID = BLAKE3(subject || predicate || object || agent || timestamp)

Same content from same agent at same time = same hash.

## Related Topics

- [Storage Layout](./storage.md)
- [Lens Resolution](./lens.md)