= Solution
Let $u_1,u_2$ be a local fundamental pair at zero, including a logarithmic Frobenius solution if the exponents are resonant. Any other independent pair on a common branch domain has $w_1=au_1+bu_2$ and $w_2=cu_1+du_2$ with constant coefficients and $ad-bc\ne0$. Bilinearity and antisymmetry of the <Wronskian> give
$$
\boxed{W(w_1,w_2)=(ad-bc)W(u_1,u_2).}
$$
Thus changing the independent branches multiplies the principal-pair <Wronskian> by a nonzero constant, once the branches are continued onto the same domain.
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