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Recently, I'm reading the paper "On the structure of spaces of Ricci curvature bounded below I" by J.Cheeger& T.Colding, I'm confused with the formula (2.20):

Suppose $(M,p)$ is a complete n-dim Riemannian manifold with $\operatorname{Ric}\geq -(n-1)$. Put $A_{r_1,r_2}(p)=B_{r_2}(p)\backslash \overline{B_{r_1}(p)}$. Fix $0<r_1<r_2$ and $0<\eta<r_1$. Let $$ X(p,r_1,,r_2,\eta)=\{q\in A_{r_1,r_2}(p)\mid \text{there exists a geodesic } \gamma \text{ with } \gamma(0)=p,\gamma(t)=q \text{ such that } \gamma|_{[0,t]} \text{ is minimal and } \gamma|_{[0,t+\eta]} \text{ is not minimal}\} $$

The authors claimed that "It follows directly from the directionally restricted version of Bishop-Gromov inequality that:" $$ \frac{\operatorname{Vol}(X(p,r_1,r_2,\eta))}{\operatorname{Vol}(B_p(1))}\leq C(n,r_1,r_2)\eta. $$ where $C=C(n,r_1,r_2)$ is a constant depending only on $n,r_1$ and $r_2$. I wonder why this holds and how directionally restricted version of Bishop-Gromov inequality is applied.

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