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docs/training/corpus/Layer_0--Primitive_Facts/CORPUS-0005-profit-is-sale-minus-total-cost.md

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+# CORPUS-0005
+## Profit Is Sale Price Minus Total Cost
+### Status: Training Corpus Seed
+### Layer: Layer_0--Primitive_Facts
+### Purpose: Teach that profit is calculated after all costs are counted, not merely by comparing purchase and sale price
+### Repository Path: docs/training/corpus/Layer_0--Primitive_Facts/CORPUS-0005-profit-is-sale-minus-total-cost.md
+
+---
+
+## 0. Principle
+
+Profit is what remains after total cost is subtracted from sale value.
+
+A trader does not profit because the sale price is higher than the purchase price.
+
+A trader profits only if the sale value exceeds every cost created by the venture.
+
+```text
+profit = sale_value - total_cost
+```
+
+---
+
+## 1. Roman-Visible Example
+
+A trader buys oil in Ostia for 10 asses.
+
+He sells it in Capua for 18 asses.
+
+At first glance, the gain appears to be 8 asses.
+
+But the venture also required:
+
+- 2 asses for porterage
+- 3 asses for cart space
+- 1 as for storage
+- 1 as for handling at Capua
+
+Total cost:
+
+```text
+10 + 2 + 3 + 1 + 1 = 17 asses
+```
+
+Actual profit:
+
+```text
+18 - 17 = 1 as
+```
+
+The venture succeeded, but only barely.
+
+---
+
+## 2. Minimal Profit Structure
+
+Profit requires at least:
+
+1. sale value
+2. purchase price
+3. movement cost
+4. holding cost
+5. transaction cost
+6. loss adjustment
+7. time and opportunity cost where relevant
+
+A sale can look profitable before the full cost is counted.
+
+---
+
+## 3. Incorrect Modern Assumption
+
+Incorrect assumption:
+
+> Bought for 10, sold for 18, profit is 8.
+
+Correction:
+
+> Bought for 10, sold for 18, profit is unknown until all costs are counted.
+
+---
+
+## 4. Simulation Use
+
+This principle supports:
+
+- venture outcome calculation
+- player feedback
+- price comparison
+- route evaluation
+- break-even analysis
+- false-profit prevention
+- training examples in Layer 1
+
+The model should always distinguish:
+
+- gross spread
+- total cost
+- actual profit
+
+---
+
+## 5. Canonical Test
+
+If the model sees:
+
+> Purchase price: 10 asses. Sale price: 18 asses.
+
+It must not immediately answer:
+
+> Profit: 8 asses.
+
+It must ask:
+
+- what was transport cost?
+- what was storage cost?
+- were dues paid?
+- was any product lost?
+- how long was capital tied up?
+- was another better venture missed?
+
+Only after total cost is known can profit be calculated.
+
+---
+
+## 6. Success Condition
+
+If the model stops treating the difference between purchase price and sale price as profit, and starts subtracting total cost from sale value, this file is functioning correctly.