H,W = map(int,input().split())
S = [input().strip() for i in range(H)]
black = []
for i in range(H):
	for j in range(W):
		if (S[i][j] == "#"):
			black.append((i,j))
		else:
			pass

if (len(black) < 2):
	print("NO")
	exit()

#黒座標を集合に変換
black_base = set(black)

# 黒マスの任意のペアを使って dx,dy を決定
for i in range(len(black)):
    x1, y1 = black[i]
    for j in range(i + 1, len(black)):
        x2, y2 = black[j]
        dx = x2 - x1
        dy = y2 - y1

        A = []
        B = []
        check = True

        # 各黒マスを 赤と青 に分類する
        for (p, q) in black:
            if (p + dx, q + dy) in black_base:
                A.append((p, q))
            elif (p - dx, q - dy) in black_base:
                B.append((p, q))
            else:
                check = False
                break

        if check and len(A) > 0 and len(B) > 0:
            print("YES")
            exit()

print("NO")