h, w = map(int, input().split())
F = [list(input()) for _ in range(h)]

for di in range(h):
    for dj in range(-w + 1, w):
        if di == 0 and dj == 0:
            continue
        C = [[None for _ in range(w)] for _ in range(h)]
        flag = True
        for i in range(h):
            for j in range(w):
                if F[i][j] == '#' and C[i][j] == None:
                    C[i][j] = 'R'
                    if 0 <= i + di < h and 0 <= j + dj < w:
                        if F[i + di][j + dj] == '#' and C[i + di][j + dj] == None:
                            C[i + di][j + dj] = 'B'
                        else:
                            flag = False
                            break
                    else:
                        flag = False
                        break
            if not flag:
                break
        if flag:
            for i in range(h):
                for j in range(w):
                    if F[i][j] == '#' and C[i][j] == None:
                        flag = False
                        break
                if not flag:
                    break
        if flag:
            print("YES")
            exit()
print("NO")