 This can be addressed for the graph example and related examples via the Yoneda Lemma as described in the Further examples section below, but this then ceases to be first-order.Topoi provide a more abstract, general, and first-order solution.As noted above, a topos "C" has a subobject classifier Ω, namely an object of "C" with an element "t" ∈ Ω, the "generic subobject" of "C", having the property that every monic "m"