"Analyzing a small part of a surface in the neighborhood of a point is called a local analysis. Though, at first glance, a local analysis may seem to be less interesting than a global analysis, time has proved otherwise." (John Tabak, "Geometry: The Language of Space and Form", 2004)
"Gauss recognized that the study of curvature of a surface in the neighborhood of a point had to be understood in order to make much progress in the study of surfaces, and one of his important contributions to differential geometry was the study of curvature. Gauss found a way to measure the curvature of a surface in a way that would enable the user to state quantitatively exactly how curved a surface is. This is harder than it may first seem, because we often confuse the curvature of a surface with that of a curve." (John Tabak, "Geometry: The Language of Space and Form", 2004)
"The fundamental concept of Gauss’s surface theory is the curvature, a quantity that is positive (and constant) for a sphere, zero for the plane and cylinder, and negative for surfaces that are 'saddle-shaped' in the neighborhood of each point." (John Stillwell, The Four Pillars of Geometry, 2000)
"Roughly speaking, a function defined on an open set of Euclidean space is differentiable at a point if we can approximate it in a neighborhood of this point by a linear map, which is called its differential (or total derivative). This differential can be of course expressed by partial derivatives, but it is the differential and not the partial derivatives that plays the central role." (Jacques Lafontaine, "An Introduction to Differential Manifolds", 2010)
"The details of the shapes of the neighborhoods are not important. If the two sets of neighborhoods satisfy the equivalence criterion, then any set that is open, closed, and so on with respect to one set of neighborhoods will be open, closed, and so on with respect to the other set of neighborhoods." (John Tabak, "Beyond Geometry: A new mathematics of space and form", 2011)
"From a narrow point of view, the precise way in which neighborhoods are specified is unimportant. As long as the resulting collection of neighborhoods satisfies the axioms that define what a topological space is, the parent set together with its neighborhoods constitute a topological space, and any such space can be studied on its own terms. From a broader point of view, given a set X, two different-looking definitions for the neighborhoods of X can sometimes result in the same topological structure - the same open sets, the same limit points, and so forth - and other times different-looking definitions for the neighborhoods of X can result in very different topological structures." (John Tabak, "Beyond geometry: a new mathematics of space and form" 2011)
"[…] topologies are determined by the way the neighborhoods are defined. Neighborhoods, not individual points, are what matter. They determine the topological structure of the parent set. In fact, in topology, the word point conveys very little information at all." (John Tabak, "Beyond Geometry: A new mathematics of space and form", 2011)
"There are many such definitions of dimension. Let me try to describe one definition of dimension. Let’s say that an 'empty object' has dimension −1. That’s an odd definition, but let’s just say that. An object has dimension n + 1 provided it has arbitrarily small neighborhoods whose boundaries have dimension n. So, for example, the real line has dimension 1 because any point in it has neighborhoods that are open intervals. The boundaries of the open intervals consist of two points, and each point is an object of dimension zero. Those two points have dimension zero because their boundary is empty." (John Tabak, "Beyond geometry: a new mathematics of space and form", 2011)
"In algebra, we defined how to operate on two elements to get another; in topology we instead define in a rough sense how close points are to each other. Specifically, beyond being a set, a topological space includes a definition of open sets or neighborhoods. This is also called defining a topology for the space." (Adam Marsh,"Mathematics for Physics: An Illustrated Handbook", 2018)
"The idea of a space covering another generalizes to any topological space: a covering space C of a space X has a continuous surjective map to X whose inverse in a neighborhood of any point of X is a union of mutually disjoint open sets homeomorphic to that neighborhood. The points that map to a point p ∈ X are called the fiber over p, and the disjoint open sets over a neighborhood of p are called sheets. Under reasonable connectivity requirements, every space then has a unique simply connected universal covering space that covers all connected covers." (Adam Marsh,"Mathematics for Physics: An Illustrated Handbook", 2018)
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