## S3 method for class 'igraph':
-(e1, e2)-difference.e2is a vertex sequence (e.g. created by theVfunction), then these vertices will be deleted from
  the graph.Efunction), then these edges will be deleted from the graph.vertex(or thevertices) function, then all arguments ofverticesare
  concatenated and the result is interpreted as a vector of vertex
  ids. These vertices will be removed from the graph.edge(or theedges) function, then all arguments ofedgesare
  concatenated and then interpreted as edges to be removed from the
  graph.
  Example:g <- make_ring(10)
V(g)$name <- letters[1:10]
E(g)$name <- LETTERS[1:10]
g <- g - edge("e|f")
g <- g - edge("H")pathfunction,
  then allpatharguments are concatenated and then interpreted
  as a path along which edges will be removed from the graph.
  Example:g <- make_ring(10)
V(g)$name <- letters[1:10]
g <- g - path("a", "b", "c", "d")+.igraph;
  add.edges, add_edges;
  add.vertices, add_vertices;
  delete.edges, delete_edges;
  delete.vertices,
  delete_vertices; edge,
  edges; path;
  vertex, vertices