1# Function Analysis
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3Functions describe **what something does**, not how. Phrasing matters: it forces the team out of solution language.
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5## Rules
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7- **Verb + noun.** Active verb, measurable noun. "Notify operator", not "notification system".
8- **One function per line.** Compound verbs hide design choices.
9- **No brand or implementation in the noun.** "Persist verdict" not "Write Postgres row".
10- **Quantify when possible.** "Bound spend <= $X/day".
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12## Classification
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14- **Basic function**  -  the reason the thing exists. Removing it kills the value.
15- **Secondary function**  -  supports, enables, protects, or pleases. Removable if a better path exists.
16- **Unnecessary function**  -  historical, habitual, performative. First candidate for cut.
17- **Required function**  -  imposed by law, contract, or policy. Cannot be cut without authority.
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19Mark each function with one tag.
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21## FAST diagram quickstart
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23Function Analysis System Technique. Read left to right: higher-order *why* on the left, lower-order *how* on the right. For each function, ask:
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25- **Why does this function exist?** -> answer is the function to its left.
26- **How is it achieved?** -> answers are the functions to its right.
27- **When else?** -> concurrent functions sit vertically.
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29Stop expanding when you reach functions whose answer is "by implementation". That column is the design boundary.
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31A skinny FAST is enough for most software work. Three columns: outcome -> primary functions -> supporting functions.
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33## Examples
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35### Software  -  antispam verdict pipeline
36- Basic: *Decide verdict* (allow|block|unclear).
37- Basic: *Persist verdict* (auditable, queryable).
38- Basic: *Bound spend* on LLM calls.
39- Secondary: *Explain verdict* to moderator.
40- Secondary: *Cache verdict* for repeat content.
41- Unnecessary: *Visualize verdict graph in admin UI*  -  historical, no decisions taken from it.
42- Required: *Retain logs >= 30 days* (policy).
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44### Non-software  -  quarterly offsite
45- Basic: *Align direction* across leads.
46- Basic: *Surface conflict* safely.
47- Secondary: *Reward team*.
48- Secondary: *Onboard new hires*.
49- Unnecessary: *Produce slide deck*  -  nobody re-reads it.
50- Required: *Stay within travel budget*.
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52## Drill question
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54Ask the user, one at a time, with *Recommended:* attached:
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56> "If we removed function X, what concretely fails?"  -  *Recommended: check if anything downstream (code, runbook, contract, user flow) actually depends on X; if no dependency surfaces from inspection, treat X as a tentative cut candidate and ask the user to confirm.*
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58Cut what survives this question. Promote what doesn't.
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