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All Odd Numbers are Prime

The mathematician says: "1 is prime, 3 is prime, 5 is prime, 7 is prime, therefore
all odd numbers are prime."

The physicist says: "1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is
... observation error ..., 11 is prime, 13 is prime, therefore all odd numbers
are prime."

The engineer says: "1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is prime,
therefore all odd numbers are prime."