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+# CORPUS-0011
+## Round-Trip Cart Value
+### Status: Training Corpus Seed
+### Layer: Layer_1--Worked_Examples
+### Purpose: Teach that transport capacity may create value in both directions, and that a route should not always be evaluated as a one-way movement
+### Repository Path: docs/training/corpus/Layer_1--Worked_Examples/CORPUS-0011-round-trip-cart-value.md
+
+---
+
+## 0. Scenario
+
+A trader in Ostia wants to send goods to Capua.
+
+A cart from Capua has already arrived in Ostia carrying raw material.
+
+The cart must return to Capua.
+
+If the trader can load the return trip, the cart owner avoids travelling empty, and the trader may obtain better terms.
+
+The same physical journey can carry value in both directions.
+
+---
+
+## 1. One-Way Assumption
+
+A weak model may treat transport as a simple one-way purchase:
+
+```text
+Ostia -> Capua cart hire = 10 asses
+```
+
+If the trader must pay the whole hire, the cost may erase profit.
+
+But if the cart already needs to return to Capua, the trader may only need to pay for unused return capacity.
+
+The cart's prior movement matters.
+
+---
+
+## 2. Known Facts
+
+| Fact | Value |
+|---|---:|
+| Cart origin | Capua |
+| Cart current location | Ostia |
+| Cart must return to Capua | yes |
+| Normal one-way hire Ostia -> Capua | 10 asses |
+| Reduced return-leg rate | 5 asses |
+| Trader's cargo value in Ostia | 20 asses |
+| Expected sale value in Capua | 32 asses |
+| Other handling costs | 3 asses |
+
+---
+
+## 3. One-Way Calculation
+
+If the trader pays full one-way hire:
+
+```text
+purchase value:      20 asses
+cart hire:           10 asses
+other handling:       3 asses
+------------------------------
+total cost:          33 asses
+sale value:          32 asses
+result:              1 as loss
+```
+
+The venture fails by arithmetic.
+
+---
+
+## 4. Return-Leg Calculation
+
+If the trader uses the cart's required return trip:
+
+```text
+purchase value:      20 asses
+return-leg rate:      5 asses
+other handling:       3 asses
+------------------------------
+total cost:          28 asses
+sale value:          32 asses
+result:              4 asses profit
+```
+
+The same cargo and destination become viable because transport capacity was already moving.
+
+---
+
+## 5. Why The Cart Owner Accepts
+
+The cart owner may accept the reduced return-leg rate because:
+
+- the cart must return to Capua anyway
+- empty return earns nothing
+- the load offsets animal feed and driver time
+- the trader pays promptly
+- the trader may offer repeat business
+- the cargo is easy to handle
+
+The reduced rate is not generosity.
+
+It is shared use of existing movement.
+
+---
+
+## 6. Round-Trip Exchange Variant
+
+The arrangement may include value in both directions:
+
+### Capua -> Ostia
+
+The cart brings:
+
+- raw timber
+- wool
+- charcoal
+- agricultural goods
+- workshop material
+
+### Ostia -> Capua
+
+The cart returns with:
+
+- oil
+- imported goods
+- tools
+- household supplies
+- finished stock
+- letters or documents
+
+Each leg may serve a different party.
+
+The trader may profit not by owning the cart, but by understanding that the cart should not return empty.
+
+---
+
+## 7. Household Supply Variant
+
+The return cargo may not all be market cargo.
+
+A Capua cart owner may ask to carry supplies for his household:
+
+- oil
+- fish sauce
+- cloth
+- tools
+- small luxury items
+- medicines or prepared goods
+
+These goods may partly settle the transport agreement.
+
+This creates a mixed exchange:
+
+```text
+cash payment
++ goods carried for household use
++ future hauling preference
+```
+
+The model should not treat household supply as irrelevant.
+
+It can be part of the transport bargain.
+
+---
+
+## 8. Risks Of Linked Legs
+
+A round-trip arrangement can fail because either leg fails.
+
+Risk examples:
+
+- inbound cargo arrives late
+- cart needs repair before return
+- animals are tired
+- driver changes terms after arrival
+- outbound cargo is not ready
+- return cargo is heavier than expected
+- goods for household use are disputed in value
+- delay on first leg destroys profit on second leg
+
+A round-trip plan may reduce cost, but it increases dependency between events.
+
+---
+
+## 9. Correct Model Behavior
+
+The model should ask:
+
+- does the cart need to return anyway?
+- is return capacity empty?
+- who controls the cart?
+- what did the cart carry inbound?
+- what can it carry outbound?
+- does return cargo reduce effective transport cost?
+- are cash, goods, and future obligations combined?
+- what risks link the two legs?
+
+Transport is not only a price.
+
+It is moving capacity across time and direction.
+
+---
+
+## 10. Incorrect Model Behavior
+
+The model should not:
+
+- treat every cart hire as isolated one-way cost
+- ignore why the cart is already in Ostia
+- ignore empty return capacity
+- ignore household supply as value
+- assume reduced rate is unexplained discount
+- ignore linked-leg risk
+- calculate each leg without considering the whole movement
+
+---
+
+## 11. Layer-0 Concepts Used
+
+This example uses:
+
+- `CORPUS-0001-trade-requires-two-locations`
+- `CORPUS-0004-cost-includes-more-than-purchase-price`
+- `CORPUS-0005-profit-is-sale-minus-total-cost`
+- `CORPUS-0006-delay-is-economic-cost`
+- `CORPUS-0009-liquidity-differs-from-wealth`
+- `CORPUS-0013-non-coin-settlement-exists`
+- `CORPUS-0018-rivalry-changes-conditions`
+
+---
+
+## 12. Success Condition
+
+If the model sees a cart moving between two cities and asks whether both directions can carry value before calculating transport cost, this file is functioning correctly.