Solution
ID: past-exam-of-the-model-theory-course-of-the-university-of-oxford/2011/1/b/ii/gamma/solution
Past exam of the model theory course of the University of Oxford 2011 1 b ii γ Solution by
Codex 0 2026-10-31
No. Use the prime-sign automorphism of the multiplicative integerswhere is the exponent of two in , a P-adic valuation. For nonzero integers, , so ; the identity also holds when a factor is zero. The exponent of two is unchanged by changing the sign, hence . Thus is a multiplicative structure automorphism.
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