other names: arc, curve, curved arc
    graph theory:
    Edges are elements of edge set E in graph G=(V, E). They are two-element subsets of set V (vertex set).
    An edge is an (connected) unordered pair of distinct verices of G. It is also a 1D cell of a complex.
    
    Edge must have 2 or 1 ends (endverices, endpoints). Set of ends is sometimes called endpoint set. If edge has 2 ends, it is "most common type of edge" and it looks like this:
    
    
    If edge has 1 end, it is called loop.
    
    The edge set of graph G is referred to as E(G). An edge e = {u, v}, where u, v`in`V is usually written as uv, e = uv.
    If uv is an edge, then we say that u and v are adjacent edges or u is neighbour of v.
    
    The edges of simple graph in `RR^3` are 1-simplexes.