 Countable random uniform hypergraph

Choose each $r$-element subset of the natural numbers as a hyperedge independently with probability $p$, where $0<p<1$. This defines a countable random uniform hypergraph. For any finite pattern in the hypergraph extension property, an outside vertex realizes it with probability $q=p^{|\mathcal{A}|}(1-p{)}^{|(\genfrac{}{}{0ex}{}{S}{r-1})\setminus \mathcal{A}|}>0$. Distinct outside vertices use disjoint edge decisions, so the probability that the first $N$ candidates all fail is $(1-q{)}^N\to 0$. Taking a countable intersection over all finite patterns proves the extension property almost surely. The bounds $0<p<1$ are necessary for all patterns to have positive probability.