Theorem10 1.4.2 is due to W. Mader, Existenz n-fach zusammenhangender Teilgraphen in Graphen genugend großer Kantendichte, Abh. Math. Sem.¨
Univ. Hamburg 37 (1972) 86–97. Theorem 1.8.1 is from L. Euler, Solution
problematis ad geometriam situs pertinentis, Comment. Acad. Sci. I. Petropolitanae 8 (1736), 128–140.