from collections import defaultdict

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


def check(dr, dc, s: set) -> bool:
    d = defaultdict(int)
    for r in range(H):
        for c in range(W):
            if (r, c) not in s: continue
            # 移動元がある
            if (r, c) in d: continue

            nr = r + dr
            nc = c + dc
            if (nr, nc) in s:  # 移動先に # がある
                d[nr, nc] = True
            else:
                return False

    return True


def solve():
    s = set()
    for i in range(H):
        for j in range(W):
            if S[i][j] == '#':
                s.add((i, j))

    if len(s) % 2 == 1:
        return False

    for i in range(H):
        for j in range(W):
            if i == 0 and j == 0: continue
            ok = check(i, j, s)
            if ok:
                return True

    return False


if solve():
    print('YES')
else:
    print('NO')