“…The Heisenberg groups (1) with fixed Lagrangian splitting (G, Γ) form a subclass within all nilquadratic extensions, corresponding to a certain subgroup H 2 G,Γ (P, T ) ≤ H 2 (P, T ) under cohomology. As for all nilquadratic extensions, the Universal Coefficient Theorem induces a short extact sequence (2) 1 G G Ext 1 (P, T ) j G G H 2 (P, T ) q G G Ω 2 (P, T ) G G 0 which splits, albeit not naturally. Here j is the natural embedding of abelian (= symmetric) cocycles while q is the skewing map [γ] → ω with ω(z, w) = γ(z, w)/γ(w, z).…”