Let $p : E \to B$ Be a continuous subjective map. An open set $U\subset B$ is considered evenly covered if $p^{-1}(U)$ is the disjoint union of some ${V_{\alpha}}$, for each $V_{\alpha}\subset E$, such that $p\mid_{V_{\alpha}} : V_{\alpha} \to U$ is a homeomorphsm. Each $V_{\alpha}$ is called a slice of $E$. If, for any $b\in B$, there exists a neighborhood $U$ containing $b$ that is evenly covere by $p$, then $p$ is a covering map.