let modulo = 1000000007
let (+@) a b = (a + b) mod modulo
let ( *@ ) a b = (a * b) mod modulo

let rec mod_pow a n =
  if n <= 0 then 1
  else if n mod 2 = 1 then a *@ mod_pow a (n-1)
  else let h = mod_pow a (n/2) in h *@ h
let mod_inv a = mod_pow a (modulo-2)

let lim = 200010

let fact =
  let res = Array.make lim 1 in
  for i = 1 to lim-1 do res.(i) <- i *@ res.(i-1) done;
  res

let inv_fact = Array.map mod_inv fact

let comb n k =
  if n < k then 0 else fact.(n) *@ inv_fact.(k) *@ inv_fact.(n-k)

let r h w = comb (h+w) h

let () =
  Scanf.scanf "%d %d %d %d" @@ fun h w a b ->
  Array.init (h-a) (fun i -> r i (b-1) *@ r (h-1-i) (w-b-1))
  |> Array.fold_left (+@) 0
  |> Printf.printf "%d\n"