The predominant design philosophy behind most Discrete Mathematics (DM) courses is that of a recycling bin: a place where mathematical prerequisites with no other natural home can live out the rest of their days in peace. This fundamentally misunderstands the role of mathematics in computer science. Instead of being a collection of topical prerequisites, mathematics provides a conceptual framework enabling the sort of high-level computational thinking that a computer science bachelor's degree is supposed to train.

Abstract In the cons-free programming paradigm, we eschew constructors and program using only destructors. Cons-free programs in a simple first-order language with string data capture exactly P, the class of polynomial-time relations. By varying the underlying language and considering other data types, we can capture several other complexity classes. However, no cons-free programming language captures any functional complexity class for fundamental reasons. In this paper, we cleanly extend the cons-free paradigm to encompass functional complexity classes. Namely, we introduce programs with data that can either only be destructed or only be constructed, which we enforce by a type system on the program variables. We call the resulting programs read/write - (or RW -)factorizable, show that RW-factorizable string programs capture exactly the class FP of polynomial-time functions, and that tail-recursive RW-factorizable programs capture exactly the class FL of logarithmic-space functions. Finally, we state and solve the nontrivial problem of syntactic composition of two RW-factorizable programs.

We exploit a decomposition of graph traversals to give a novel characterization of depth-first and breadth-first traversals as universal constructions. Specifically, we introduce functors from two different categories of edge-ordered directed graphs into two different categories of transitively closed edge-ordered graphs; one defines the lexicographic depth-first traversal and the other the lexicographic breadth-first traversal. We show that each functor factors as a composition of universal constructions, and that the usual presentation of traversals as linear orders on vertices can be recovered with the addition of an inclusion functor. Finally, we raise the question of to what extent we can recover search algorithms from the categorical description of the traversal they compute.

Abstract We define a new type of “shatter function” for set systems that satisfies a Sauer–Shelah type dichotomy, but whose polynomial-growth case is governed by Shelah’s two-rank instead of VC dimension. We identify the least exponent bounding the rate of growth of the shatter function, the quantity analogous to VC density, with Shelah’s $\omega $ -rank.