ScalingStacks

Proposition 6.5 . [04K8]

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Proposition 6.5.

Let f:X→Bf:X\rightarrow B be a stitched fibration and let γ±\gamma^{\pm} be bases of H1​(X,ℤ)H_{1}(X,\mathbb{Z}) satisfying the above conditions. Then the restrictions of γ±\gamma^{\pm} to H1​(X±,ℤ)H_{1}(X^{\pm},\mathbb{Z}) induce embeddings,

Λ±↪TB±∗.\Lambda^{\pm}\hookrightarrow T^{\ast}_{B^{\pm}}.

Let α±:B±→ℝn\alpha^{\pm}:B^{\pm}\rightarrow\mathbb{R}^{n} be the corresponding action coordinates satisfying α±​(b)=0\alpha^{\pm}(b)=0 for some b∈Γb\in\Gamma. Then the map

α={α+on​B+α−on​B−\alpha=\begin{cases}\alpha^{+}&\textrm{on}\ B^{+}\\ \alpha^{-}&\textrm{on}\ B^{-}\end{cases}

is an admissible change of coordinates. If b1,…​bnb_{1},\ldots b_{n} denote the action coordinates on BB given by α\alpha, then {d​b1,…​d​bn}\{db_{1},\ldots db_{n}\} is a basis of Λ+\Lambda^{+} and Λ−\Lambda^{-}. Furthermore, the reduced space Z¯\bar{Z} can be identified with T∗​Γ/⟨d​b2,…,d​bn⟩ℤT^{\ast}\Gamma/\penalty\langle db_{2},\ldots,db_{n}\rangle_{\mathbb{Z}} and the reduced fibration f¯\bar{f} can be identified with the standard projection π¯\bar{\pi}. Moreover ℓ1\ell_{1} satisfies

∫[d​bj]ℓ1=mj,j=2,…,n\int_{[db_{j}]}\ell_{1}=m_{j},\quad j=2,\ldots,n (49)

where [d​bj]∈H1​(Z¯,ℤ)[db_{j}]\in H_{1}(\bar{Z},\mathbb{Z}) is the class represented by d​bjdb_{j}.

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