use std::collections::VecDeque;

fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let xx: Vec<Vec<char>> = xx
        .split_whitespace()
        .skip(2)
        .map(|s| s.chars().collect())
        .collect();

    let mut blk = VecDeque::new();
    for y in 0..xx.len() {
        for x in 0..xx[0].len() {
            if xx[y][x] == '#' {
                blk.push_back((y, x));
            }
        }
    }
    let blk = blk;

    if blk.len() & 1 == 1 {
        println!("NO");
        return;
    }

    'outer: for i in 1..blk.len() {
        let (dy, dx) = (blk[i].0 - blk[0].0, blk[i].1 - blk[0].1);

        let mut tmp = blk.clone();
        while !tmp.is_empty() {
            let (y, x) = tmp.pop_front().unwrap();
            let moves_to = (y + dy, x + dx);
            if tmp.contains(&moves_to) {
                tmp.retain(|c| c != &moves_to);
            } else {
                continue 'outer;
            }
        }

        println!("YES");
        return;
    }

    println!("NO");
}