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Abstract

Let $\pi: E \to B$ be a fiber bundle with fiber having the mod~2 cohomology algebra of a real or a complex projective space and let $\pi': E' \to B$ be a vector bundle such that $\mathbb{Z}_2$ acts fiber preserving and freely on $E$ and $E'-0$, where $0$ stands for the zero section of the bundle $\pi':E' \to B$. For a fiber preserving $\mathbb{Z}_2$-equivariant map $f:E \to E'$, we estimate the cohomological dimension of the zero set $Z_f = \{x \in E \mid f(x)= 0\}.$ As an application, we also estimate the cohomological dimension of the $\mathbb{Z}_2$-coincidence set $A_f=\{x \in E\mid f(x) = f(T(x)) \}$ of a fiber preserving map $f:E \to E'$.