文摘
A hyperplane of the symplectic dual polar space 0f9da144bfc69630b38688876bc4c52" title="Click to view the MathML source">DW(2n−1,F), n≥2, is said to be of subspace-type if it consists of all maximal singular subspaces of W(2n−1,F) meeting a given (n−1)-dimensional subspace of 208a490b4329a368ef0c4d7ab16" title="Click to view the MathML source">PG(2n−1,F). We show that a hyperplane of 0f9da144bfc69630b38688876bc4c52" title="Click to view the MathML source">DW(2n−1,F) is of subspace-type if and only if every hex 0f1d2f782679f261892fc1" title="Click to view the MathML source">F of 0f9da144bfc69630b38688876bc4c52" title="Click to view the MathML source">DW(2n−1,F) intersects it in either 0f1d2f782679f261892fc1" title="Click to view the MathML source">F, a singular hyperplane of 0f1d2f782679f261892fc1" title="Click to view the MathML source">F or the extension of a full subgrid of a quad. In the case F is a perfect field of characteristic 2, a stronger result can be proved, namely a hyperplane H of 0f9da144bfc69630b38688876bc4c52" title="Click to view the MathML source">DW(2n−1,F) is of subspace-type or arises from the spin-embedding of f45af289c61072" title="Click to view the MathML source">DW(2n−1,F)≅DQ(2n,F) if and only if every hex 0f1d2f782679f261892fc1" title="Click to view the MathML source">F intersects it in either 0f1d2f782679f261892fc1" title="Click to view the MathML source">F, a singular hyperplane of 0f1d2f782679f261892fc1" title="Click to view the MathML source">F, a hexagonal hyperplane of 0f1d2f782679f261892fc1" title="Click to view the MathML source">F or the extension of a full subgrid of a quad.