The genus series for maps is the generating series for the number of rooted maps with a given number of vertices and faces of each degree, and a given number of edges. It captures topological information about surfaces, and appears in questions arising in statistical mechanics, topology, group rings, and certain aspects of free probability theory. An expression has been given previously for the genus series for maps in locally orientable surfaces in terms of zonal polynomials. The purpose of this paper is to derive an integral representation for the genus series. We then show how this can be used in conjunction with integration techniques to determine the genus series for monopoles in locally orientable surfaces. This complements the analogous result for monopoles in orientable surfaces previously obtained by Harer and Zagier. A conjecture, subsequently proved by Okounkov, is given for the evaluation of an expectation operator acting on the Jack symmetric function. It specialises to known results for Schur functions and zonal polynomials.

We prove an integration formula involving Jack polynomials conjectured by I.~P.~Goulden and D.~M.~Jackson in connection with enumeration of maps in surfaces.

Using Feferman-Vaught techniques a condition on the fine spectrum of an admissible class of structures is found which leads to a first-order 0--1 law. The condition presented is best possible in the sense that if it is violated then one can find an admissible class with the same fine spectrum which does not have a first-order 0--1 law. If the condition is satisfied (and hence we have a first-order %% 0--1 law)

In the genus polynomial of the graph $G$, the coefficient of $x^k$ is the number of distinct embeddings of the graph $G$ on the oriented surface of genus $k$. It is shown that for several infinite families of graphs all the zeros of the genus polynomial are real and negative. This implies that their coefficients, which constitute the genus distribution of the graph, are log concave and therefore also unimodal. The geometric distribution of the zeros of some of these polynomials is also investigated and some new genus polynomials are presented.

Using Feferman-Vaught techniques we show a certain property of the fine spectrum of an admissible class of structures leads to a first-order law. The condition presented is best possible in the sense that if it is violated then one can find an admissible class with the same fine spectrum which does not have a first-order law. We present three conditions for verifying that the above property actually holds. The first condition is that the count function of an admissible class has regular variation with a certain uniformity of convergence. This applies to a wide range of admissible classes, including those satisfying Knopfmacher's Axiom A, and those satisfying Bateman and Diamond's condition. The second condition is similar to the first condition, but designed to handle the discrete case, {\it i.e.}, when the sizes of the structures in an admissible class $K$ are all powers of a single integer. It applies when either the class of indecomposables or the whole class satisfies Knopfmacher's Axiom A$^\#$. The third condition is also for the discrete case, when there is a uniform bound on the number of $K$-indecomposables of any given size.

Symplectic and orthogonal Schur functions can be defined combinatorially in a manner similar to the classical Schur functions. This paper demonstrates that they can also be expressed as determinants. These determinants are generated using planar decompositions of tableaux into strips and the equivalence of these determinants to symplectic or orthogonal Schur functions is established by Gessel-Viennot lattice path techniques. Results for rational (also called {\it composite}) Schur functions are also obtained.

We give several new characterizations of Riordan Arrays, the most important of which is: if $\{d_{n,k}\}_{n,k \in {\bf N}}$ is a lower triangular array whose generic element $d_{n,k}$ linearly depends on the elements in a well-defined though large area of the array, then $\{d_{n,k}\}_{n,k \in {\bf N}}$ is Riordan. We also provide some applications of these characterizations to the lattice path theory.

In the present paper, we face the problem of classifying classes of orientable PL $5$-manifolds $M^5$ with $h \geq 1$ boundary components, by making use of a combinatorial invariant called {\it regular genus} ${\cal G}(M^5)$. In particular, a complete classification up to regular genus five is obtained: $${\cal G}(M^5) = \gG \leq 5 \Longrightarrow M^5 \cong \#_{\varrho - \gbG}(\bdo) \# \smo_{\gbG},$$ where $\gbG = {\cal G}(\partial M^5)$ denotes the regular genus of the boundary $\partial M^5$ and $\smo_{\gbG}$ denotes the connected sum of $h\geq 1$ orientable $5$-dimensional handlebodies $\cmo_{\alpha_i}$ of genus $\alpha_i\geq 0$ ($i=1,\ldots, h$), so that $\sum_{i=1}^h \alpha_i = \gbG.$ \par Moreover, we give the following characterizations of orientable PL $5$-manifolds $M^5$ with boundary satisfying particular conditions related to the ``gap'' between ${\cal G}(M^5)$ and either ${\cal G}(\partial M^5)$ or the rank of their fundamental group $\rk\bigl(\pi_1(M^5)\bigr)$: $$\displaylines{{\cal G}(\partial M^5)= {\cal G}(M^5) = \varrho \Longleftrightarrow M^5 \cong \smo_{\gG}\cr {\cal G}(\partial M^5)= \gbG = {\cal G}(M^5)-1 \Longleftrightarrow M^5 \cong (\bdo) \# \smo_{\gbG}\cr {\cal G}(\partial M^5)= \gbG = {\cal G}(M^5)-2 \Longleftrightarrow M^5 \cong \#_2 (\bdo) \# \smo_{\gbG}\cr {\cal G}(M^5) = \rk\bigl(\pi_1(M^5)\bigr)= \varrho \Longleftrightarrow M^5 \cong \#_{\gG - \gbG}(\bdo) \# \smo_{\gbG}.\cr}$$ \par Further, the paper explains how the above results (together with other known properties of regular genus of PL manifolds) may lead to a combinatorial approach to $3$-dimensional Poincar\'e Conjecture.