v10.18.0 — no Q=-1 q-difference relation for U,V (P3)

U and V satisfy no linear q-difference relation A0(x)f(x)+A1(x)f(-x)=b(x) with Q=-1 (paper2a cor:Qminusone). PROVED, conditional on cor:arcUV (hence on thm:model and thm:RJ). The proof uses a 2-adic valuation argument at odd-order arc points; the delicate steps were independently reverified in PARI/GP exact algebraic number theory by Reviewer AG, who found no false step. Three minor exposition/script fixes applied.