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We consider a generalised model of a random simplicial complex, which arises from a random hypergraph. Our model is generated by taking the downward-closure of a non-uniform binomial random hypergraph, in which for each $k$, each set of $k+1$ vertices forms an edge with some probability $p_k$ independently. As a special case, this contains an extensively studied model of a (uniform) random simplicial complex, introduced by Meshulam and Wallach [Random Structures & Algorithms 34 (2009), no. 3, pp. 408-417]. We consider a higher-dimensional notion of connectedness on this new model according to the vanishing of cohomology groups over an arbitrary abelian group $R$. We prove that this notion of connectedness displays a phase transition and determine the threshold. We also prove a hitting time result for a natural process interpretation, in which simplices and their downward-closure are added one by one. In addition, we determine the asymptotic behaviour of cohomology groups inside the critical window around the time of the phase transition., 57 pages

We derive a decomposition scheme of unlabelled triangulations rooted at a single cell, where the decomposition depends on whether the automorphism group of the triangulation contains reflections, rotations, or both. Furthermore, the decomposition scheme is constructive in the sense that for each of the three cases, there is a $k\in\mathbb{N}$ such that the scheme defines a one-to-$k$ correspondence between the respective triangulations and their decompositions.

Given an assignment of weights $w$ to the edges of an infinite graph $G$, a matching $M$ in $G$ is called strongly $w$-maximal if for any matching $N$ there holds $\sum\{w(e) \mid e \in N \setminus M\} \le \sum\{w(e) \mid e \in M \setminus N\}$. We prove that if $w$ assumes only finitely many values all of which are rational then $G$ has a strongly $w$-maximal matching. This result is best possible in the sense that if we allow irrational values or infinitely many values then there need not be a strongly $w$-maximal matching.