def t(H, W, S):
    for dy in range(H):
        for dx in range(W):
            bs = list(S)
            for y in range(H - dy):
                for x in range(W - dx):
                    x1 = 1 << x
                    x1dx = x1 << dx
                    if bs[y] & x1:
                        bs[y] -= x1
                        bs[y + dy] -= x1dx
            if all(b == 0 for b in bs):
                return True


def solve():
    H, W = list(map(int, input().split()))
    S = [0] * H

    for i in range(H):
        s = input()
        S[i] = sum(1 << i for i in range(W) if s[i] == '#')

    if sum(S) == 0:
        return False

    return t(H, W, S) or t(H, W, S[::-1])


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


if __name__ == '__main__':
    main()