#![allow(dead_code, unused_variables, unused_macros)]

fn solve(blacks: Vec<(i32, i32)>) -> bool {
    if blacks.len() % 2 != 0 {
        return false;
    }
    let (tx, ty) = blacks[0];
    for (x, y) in blacks.iter().skip(1) {
        let (dx, dy) = (tx - *x, ty - *y);

        let count = blacks
            .iter()
            .filter(|(x, y)| {
                blacks.contains(&(*x + dx, *y + dy)) || blacks.contains(&(*x - dx, *y - dy))
            })
            .count();
        if count == blacks.len() {
            return true;
        }
    }
    false
}

fn main() {
    input!(h:usize,w:usize,s:[chars;h]);
    let blacks: Vec<_> = s
        .into_iter()
        .enumerate()
        .flat_map(|(y, vc)| vc.into_iter().enumerate().map(move |(x, c)| (x, y, c)))
        .filter_map(|(x, y, c)| (c == '#').then_some((x as i32, y as i32)))
        .collect();

    let ans = if solve(blacks) { "YES" } else { "NO" };
    println!("{ans}");
}

mod xxx {
    // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
    #[macro_export]
    macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s;
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}
    #[macro_export]
    macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

    #[macro_export]
    macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, bits)=>{
        u64::from_str_radix(&$next(), 2).expect("Parse error")
    };

    ($next:expr, hexs)=>{
        u64::from_str_radix(&$next(), 16).expect("Parse error")
    };


    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}
}