#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>

using vii = std::vector<std::pair<int,int>>;

template<class TupleT>
TupleT diff(TupleT l, TupleT r)
{
    return {std::get<0>(l) - std::get<0>(r), std::get<1>(l) - std::get<1>(r)};
}

template<class TupleT>
TupleT add(TupleT l, TupleT r)
{
    return {std::get<0>(l) + std::get<0>(r), std::get<1>(l) + std::get<1>(r)};
}

bool f2(vii blacks, size_t firstI, size_t firstJ)
{
    std::pair d = diff(blacks[firstJ], blacks[firstI]);
    std::vector<bool> used(blacks.size(), false);
    used[firstI] = true;
    used[firstJ] = true;

    for (size_t i = 0; i < blacks.size(); i++)
    {
        if (used[i]) continue;
        std::pair expected = add(blacks[i], d);
        auto it = std::lower_bound(begin(blacks), end(blacks), expected);
        
        if (it != end(blacks) && *it == expected)
        {
            int j = it - begin(blacks);
            used[j] = true;
        }
        else
        {
            return false;
        }
        
    }
    
    return true;
}

bool f(const vii &blacks)
{
    size_t B = blacks.size();
    if (B % 2 != 0) return false;

    bool ret = false;
    for (size_t i = 1; i < B; i++)
    {
        ret = ret || f2(blacks, 0, i);
    }
    return ret;
}

int main()
{
    int H, W;
    std::cin >> H >> W;
    vii blacks;
    for (int h = 0; h < H; h++)
    {
        std::string S;
        std::cin >> S;
        for (int w = 0; w < W; w++)
        {
            if (S[w] == '#') blacks.emplace_back(h, w);
        }
    }

    bool ans = f(blacks);
    const char *anss = ans ? "YES" : "NO";
    std::cout << anss << std::endl;
}