{-# LANGUAGE RankNTypes #-}
    
import Control.Monad.State
import Control.Monad.ST
import Data.Array.ST
import Control.Arrow
import Control.Monad
import Data.List
import qualified Data.ByteString.Char8 as B
import Data.Foldable
--import Debug.Trace

main :: IO ()
main = readLine >>= print . solve

solve :: [Int] -> Int
solve [h, w, a, b] = runST (initialize >>= stAction)
    where
        initialize :: ST s (Table s Int Int)
        initialize = newArray (0, h + w) Nothing
        
        stAction = evalStateT calc 

        calc = sum' <$> mapM count [1..(h - a)]

        count i = mul <$> cmb (i - 1) (b - 1) <*> cmb (h - i) (w - b - 1)

        cmb x y = prod <$> sequence [frac $ x + y, inv <$> frac x, inv <$> frac y]

        frac = memoizeFix memFrac
            where
                memFrac f n
                    | n > 0 = mul n <$> f (n - 1)
                    | otherwise = return 1

        prod = foldl' mul 1
        sum' = foldl' add 0

readLine :: IO [Int]
readLine = unfoldr (fmap (second (maybe B.empty snd . B.uncons)) . B.readInt) <$> B.getLine

readContents :: Int -> IO [[Int]]
readContents = flip replicateM readLine

infixl 6 `add`
infixl 7 `mul`

add :: Int -> Int -> Int
add x y = val $ x + y

mul :: Int -> Int -> Int
mul x y = val $ x * y

inv :: Int -> Int
inv x = pow x $ modVal - 2

pow :: Int -> Int -> Int
pow b e
    | e == 0 = 1
    | odd e = mul b . pow b $ e - 1
    | otherwise = mul v v
    where
        v = pow b $ e `div` 2

val :: Int -> Int
val = (`mod` modVal)

modVal :: Int
modVal = 10 ^ 9 + 7

primes :: [Int]
primes = build [2..]
    where
        build (x : xs) = x : build (filter (\n -> n `mod` x /= 0) xs)
        
isPrime :: Int -> Bool
isPrime n = check primes
    where
        check (x : xs)
            | x == n = True
            | x > n = False
            | otherwise = check xs

type Table s a b = STArray s a (Maybe b)
type Memo s a b = a -> StateT (Table s a b) (ST s) b

evalMemo :: (Ix a) => (forall s. Memo s a b -> Memo s a b) -> a -> Table s a b -> ST s b
evalMemo f k = evalStateT (memoizeFix f k)

runMemo :: (Ix a) => (forall s. Memo s a b -> Memo s a b) -> a -> Table s a b -> ST s (b, Table s a b)
runMemo f k = runStateT (memoizeFix f k)

memoizeFix :: (Ix a) => (forall s. Memo s a b -> Memo s a b) -> forall s. Memo s a b
memoizeFix f k = get >>= (\arr -> lift (readArray arr k) >>= maybe (f (memoizeFix f) k >>= ((<$) <*> (lift . writeArray arr k . Just))) return)