def is_valid(y,x,board):
    h = len(board)
    w = len(board[0])

    if not (0 <= y < h):
        return False
    
    if not (0 <= x < w):
        return False
    
    if board[y][x] == ".":
        return False
    
    return True

def check(board,dy,dx,black_count):
    h = len(board)
    w = len(board[0])
    used = set()
    for y in range(h):
        for x in range(w):
            if board[y][x] == ".":
                continue
            if (y,x) in used:
                continue

            if not is_valid(y+dy,x+dx,board):
                return False
            black_count -= 2
            used.add((y+dy,x+dx))
    
    if black_count > 0:
        return False
    return True



def main():
    h,w = map(int,input().split()) 
    board = []
    black_count = 0
    for _ in range(h):
        line:list = list(input())
        board.append(line)
        black_count += line.count("#")
    if black_count == 0:
        print("NO")
        return
    for dy in range(h):
        for dx in range(-w,w):
            if dy == 0 and dx == 0:
                continue
            if check(board,dy,dx,black_count):
                print("YES")
                return
    
    print("NO")
    return

main()