We determine all homogeneous pseudo-embeddings of the affine space AG(n, 4) and the projective space PG(n, 4). We give a classification of all pseudo-hyperplanes of AG(n, 4). We also prove that the two homogeneous pseudo-embeddings of the generalized quadrangle Q(4, 3) are induced by the two homogeneous pseudo-embeddings of AG(4, 4) into which Q(4, 3) is fully embeddable.Keywords: homogeneous pseudo-embedding, pseudo-hyperplane MSC2000: 51E20, 05B25
Basic definitions and main resultsThe aim of this section is to state the main results of this paper and to define the basic notions which are necessary to understand these results. Throughout this section, S = (P, L, I) is a point-line geometry with the property that the number of points on each line is finite and at least three.Suppose V is a vector space over the field F 2 of order 2. A pseudo-embedding of S into the projective space Σ = PG(V ) is a mapping e from P to the point set of Σ satisfying: (1) < e(P) > Σ = Σ; (2) if L is a line of S with points x 1 , x 2 , . . . , x k , then the points e(x 1 ), e(x 2 ), . . . , e(x k−1 ) of Σ are linearly independent and e(x k ) = wherev i , i ∈ {1, 2, . . . , k − 1}, is the unique vector of V for which e(x i ) = Σ . Two pseudo-embeddings e 1 : S → Σ 1 and e 2 : S → Σ 2 of S are called isomorphic (e 1 ∼ = e 2 ) if there exists an isomorphism φ : Σ 1 → Σ 2 such that e 2 = φ • e 1 . The notion pseudoembedding was introduced in De Bruyn [1].Suppose e : S → PG(V ) is a pseudo-embedding of S and G is a group of automorphisms of S. We say that e is G-homogeneous if for every θ ∈ G, there exists a (necessarily unique) projectivity η θ of PG(V ) such that e(x θ ) = e(x) η θ for every point x of S. If G is the full automorphism group of S, then e is also called a homogeneous pseudo-embedding.Suppose e : S → Σ is a pseudo-embedding of S and α is a subspace of Σ satisfying the following two properties: 1