N,M = [ int(it) for it in input().split() ]
li = [[ 1 if it=="#" else 0 for it in input() ]  for i in range(N)] 

flag = False
for i in range(N):
  for j in range(M):
    if (i+1<N):
      if (li[i][j]==li[i+1][j]):
        flag = True
    if (j+1<M):
      if (li[i][j]==li[i][j+1]):
        flag = True
print ( "Yes" if flag else "No"  )
    