H, W = map(int, input().split())
S = [input() for _ in range(H)]

def func(ty, tx):
    if tx == 0 and ty == 0:
        return False
    CL = [[False] * W for _ in range(H)]
    for y in range(H):
        for x in range(W):
            if S[y][x] == "#" and CL[y][x] == False:
                if x+tx >= W or x+tx < 0 or y+ty >= H:
                    return False
                if S[y+ty][x+tx] == "#" and CL[y+ty][x+tx] == False:
                    CL[y][x] = True
                    CL[y+ty][x+tx] = True
                else:
                    return False
    return True

for ty in range(H):
    for tx in range(-W+1,W):
        if func(ty, tx):
            print("YES")
            exit()

print("NO")