ABSTRACT
This chapter discusses a diagraph, which includes some of each kind of path and circuits. A non-directed multigraph has an Euler path if and only if it is connected and has exactly 2 vertices of add degree. In the latter case, the two vertices of odd degree are the end points of every Euler path in the multigraph. Moreover, every time the Euler path meets a vertex it traverses two edges which are incident on the vertex and which have not been traced before. The chapter discusses some basic rules for constructing Hamiltonian paths and cycles.
