from copy import deepcopy


def search(yi, xi):
    global overy
    global overx
    SC = deepcopy(S)
    yt = 0
    while(yt < H):
        xt = 0
        while(xt < W):
            if SC[yt][xt] == "#":
                try:
                    if SC[yt+yi][xt+xi] == "#":
                        SC[yt+yi][xt+xi] = "$"
                    else:
                        return False
                except IndexError:
                    if yt+yi >= H:
                        overy = yi
                    if xt+xi >= W:
                        overx = xi
                    return False
            xt += 1
        yt += 1
    return True


H, W = list(map(int, input().split()))
S = [0] * H
for i in range(H):
    S[i] = list(input())
printed = False
y = 0
overy, overx = float("inf"), float("inf")
while(y < H):
    x = 0
    while(x < W):
        if S[y][x] == "#":
            yi = -y
            while(y + yi < H):
                xi = -x
                while(x + xi < W):
                    if yi != 0 or xi != 0:
                        if S[y+yi][x+xi] == "#":
                            if search(yi, xi):
                                yi, xi = float("inf"), float("inf")
                                print("YES")
                                printed = True
                    xi += 1
                    if overx < xi:
                        xi = float("inf")
                yi += 1
                if overy < yi:
                    yi = float("inf")
            y, x = float("inf"), float("inf")
        x += 1
    y += 1
    if y >= H and not printed:
        print("NO")