from copy import deepcopy

H, W = map(int, input().split())
S = [list(input()) for _ in range(H)]
for i in range(H):
    for j in range(W):
        if i == 0 and j == 0:
            continue
        T = deepcopy(S)
        f = True
        for h in range(H):
            for w in range(W):
                if T[h][w] == "#":
                    T[h][w] == "."
                    if i + h < H and j + w < W:
                        if T[i + h][j + w] == "#":
                            T[i + h][j + w] = "."
                        else:
                            f = False
                    else:
                        f = False
                if f == False:
                    break
            if f == False:
                break
        if f == True:
            print("YES")
            exit()
print("NO")