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+# CORPUS-0002
+## One-As Margin And Break-Even
+### Status: Training Corpus Seed
+### Layer: Layer_1--Worked_Examples
+### Purpose: Teach that a tiny sale margin can disappear once small costs, delay, or loss are counted
+### Repository Path: docs/training/corpus/Layer_1--Worked_Examples/CORPUS-0002-one-as-margin-and-break-even.md
+
+---
+
+## 0. Scenario
+
+A trader buys a small good in Ostia for 3 asses.
+
+He expects to sell it in Capua for 4 asses.
+
+At first glance, the venture appears profitable.
+
+The expected spread is only 1 as.
+
+A one-as margin is fragile.  
+Almost any additional cost can erase it.
+
+---
+
+## 1. Known Facts
+
+| Fact | Value |
+|---|---:|
+| Origin | Ostia |
+| Destination | Capua |
+| Purchase price | 3 asses |
+| Expected sale price | 4 asses |
+| Gross spread | 1 as |
+
+---
+
+## 2. First Incorrect Calculation
+
+A weak model may calculate:
+
+```text
+4 asses - 3 asses = 1 as profit
+```
+
+This is incomplete.
+
+The calculation ignores every cost required to move, hold, protect, or sell the good.
+
+---
+
+## 3. Break-Even Point
+
+The trader breaks even only if total cost is 4 asses or less.
+
+```text
+sale value = 4 asses
+break-even total cost = 4 asses
+```
+
+Since the purchase price is already 3 asses, the trader can spend only 1 additional as before profit disappears.
+
+```text
+maximum additional cost before loss = 1 as
+```
+
+---
+
+## 4. Cost Variants
+
+### Variant A — No Added Cost
+
+```text
+purchase price = 3 asses
+sale value = 4 asses
+profit = 1 as
+```
+
+The venture succeeds.
+
+### Variant B — One Additional As
+
+```text
+purchase price = 3 asses
+handling = 1 as
+total cost = 4 asses
+sale value = 4 asses
+profit = 0
+```
+
+The venture breaks even.
+
+### Variant C — Two Additional Asses
+
+```text
+purchase price = 3 asses
+handling + delay = 2 asses
+total cost = 5 asses
+sale value = 4 asses
+loss = 1 as
+```
+
+The venture fails.
+
+---
+
+## 5. Why Small Margins Matter
+
+A small margin is not useless.
+
+It may still be acceptable if:
+
+- the trader is already sending a cart
+- the good fills unused space
+- the sale builds trust
+- the buyer may become a repeat contact
+- the good is part of a larger bundle
+- the trader has no better use for the coin
+
+But a small margin is dangerous if:
+
+- transport must be paid separately
+- storage is uncertain
+- delay is likely
+- the destination price is stale
+- the buyer may refuse
+- rivals may arrive first
+
+---
+
+## 6. Correct Model Behavior
+
+The model should reason:
+
+- a one-as spread is not automatically profit
+- break-even depends on total cost
+- tiny margins are fragile
+- low-value goods may still matter when bundled
+- context determines whether small gain is worth risk
+
+---
+
+## 7. Incorrect Model Behavior
+
+The model should not:
+
+- treat every positive spread as safe profit
+- ignore small costs because they look minor
+- assume one-as profit is always worth pursuing
+- assume tiny trades are meaningless
+- ignore bundling, repeat contact, or unused capacity
+
+---
+
+## 8. Layer-0 Concepts Used
+
+This example uses:
+
+- `CORPUS-0002-goods-have-local-prices`
+- `CORPUS-0003-money-has-purchasing-power`
+- `CORPUS-0004-cost-includes-more-than-purchase-price`
+- `CORPUS-0005-profit-is-sale-minus-total-cost`
+- `CORPUS-0006-delay-is-economic-cost`
+- `CORPUS-0012-every-venture-risks-loss`
+
+---
+
+## 9. Success Condition
+
+If the model sees a one-as spread and immediately asks whether total cost leaves any margin, this file is functioning correctly.