# once (temporal)

a change that happened a single time in the previous

- Computed level: L5 (depth in the emergence graph, not abstraction)
- Status: review  ·  Domain: temporal  ·  Arena: once

## Emergence
**Emerges from:** [single](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-single.quantity), [change](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-change.process), [previous](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-previous.temporal), [time](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-time.dimension), [happen](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-happen.event-occurrence)

**Through:** a single change occurs before now

**Novel properties:**
- singular past occurrence
- completed change instance
- temporally bounded event

## Examples
- The Chicxulub impact altered Earth's climate within hours, ending the Cretaceous period 66 million years ago. *(geology)*
- The 2003 Northeast blackout began with a single relay failure in Ohio, cascading to 55 million people. *(engineering)*
- The Bitcoin network adjusted its difficulty for the first time on January 9, 2009, after block 24. *(computing)*

## Used by
- [integrity](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-integrity.state) (L18)
- [proportion](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-proportion.relation) (L18)

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*Canonical: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-once.temporal*  
*Structured data: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-once.temporal.json*  
*Every definition provably resolves to space, time, energy and pattern.*