c n k=product[n-k+1..n]`div`product[1..k]
main=do
 [h,w,a,b]<-map read.words<$>getLine
 print$(sum[(((c (a+w-b) (w-b-x))`mod`(10^9+7))*((c (h-a+b) (h-a-x))`mod`(10^9+7)))`mod`(10^9+7)|x<-[0..min(w-b h-a)]])`mod`(10^9+7)
 