“…Let a be a Lie superalgebra (in particular, a Lie algebra) equipped with a non-degenerate invariant supersymmetric bilinear form B a , suggestively abbreviated to NIS superalgebra in [BKLS], defined over a field K of positive characteristic p. The notion of a double extension of the Lie superalgebra a, called D-extension in [BeBou], was introduced by Medina and Revoy [MR] in the case of Lie algebras. This notion has been superized and studied in a series of papers [ABB,ABBQ,BBB,BB,B,B2,BeBou]. The double extension of a, denoted by g, simultaneously involves three ingredients:…”