On embeddings of Grassmann graphs in polar Grassmann graphs

Abstract

We establish that every embedding of a Grassmann graph in a polar Grassmann graph can be reduced to an embedding in a Grassmann graph or to an embedding in the collinearity graph of a polar space. Also, we consider $3$-embeddings, i.e. embeddings preserving all distances not greater than $3$, of dual polar graphs whose diameter is not less than $3$ in polar Grassmann graphs formed by non-maximal singular subspaces. Using the same arguments we show that every such an embedding can be reduced to an embedding in a Grassmann graph.