Keep a One-Way Rule Pointing the Right Way - Practice 1

A statement if P then Q does not by itself establish if Q then P.

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A statement if P then Q does not by itself establish if Q then P. Test the direction: other conditions might also produce Q. Treat the fictional rules as supplied assumptions, not real policies.

Worked example

If a card is gold, it is valid does not imply every valid card is gold. Other valid colors may exist.

Would you believe it?

Counting entry events and counting distinct visitors can produce different totals without a contradiction.

Question 1 Fictional rule: every gold permit is valid. Nothing is said about other colors. Which conclusion follows? A gold permit is valid. Every valid permit is gold. No other color can be valid.

Question 2 Fictional rule: every blue permit is valid. Nothing is said about other colors. Which conclusion follows? Every valid permit is blue. No other color can be valid. A blue permit is valid.

Question 3 Fictional rule: every green permit is valid. Nothing is said about other colors. Which conclusion follows? No other color can be valid. A green permit is valid. Every valid permit is green.

Question 4 Fictional rule: every red permit is valid. Nothing is said about other colors. Which conclusion follows? A red permit is valid. Every valid permit is red. No other color can be valid.

Question 5 Fictional rule: every silver permit is valid. Nothing is said about other colors. Which conclusion follows? Every valid permit is silver. No other color can be valid. A silver permit is valid.

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