The formal study of combinatorics dates at least to Gottfried Wilhelm Leibniz’s Dissertatio de Arte Combinatoria in the seventeenth
century. The last half-century, however, has seen a huge growth in the subject, fueled by problems and applications from many
fields of study.
[Combinatorics] has emerged as a new subject standing at the crossroads between pure and applied mathematics, the center of
bustling activity, a simmering pot of new problems and exciting speculations.
– Gian-Carlo Rota, [243, p. vii]