set G2 = the Subgraph of G;
set G3 = the Subgraph of G | _GraphSelectors;
reconsider G3 = the Subgraph of G | _GraphSelectors as Subgraph of G by GLIB_000:128, GLIB_000:92;
take G3 ; :: thesis: G3 is plain
thus G3 is plain ; :: thesis: verum