package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func main() {
	sc.Split(bufio.ScanWords)
	h, w := nextInt(), nextInt()
	m := make([][]byte, h)
	for i := range m {
		m[i] = []byte(nextLine())
	}

	for i := 0; i < h; i++ {
		for j := 0; j < w; j++ {
			if i == 0 && j == 0 {
				continue
			}
			isPh, isPw := true, true
			if j != 0 {
				for k := 0; k < h; k++ {
					c := 0
					for x, y := 0, k; x < w && y < h; x, y = x+j, y+i {
						if m[y][x] == '#' {
							c++
						}
					}
					if c%2 == 1 {
						isPh = false
						break
					}
				}
			}

			if i != 0 {
				for k := 0; k < w; k++ {
					c := 0
					for x, y := k, 0; x < w && y < h; x, y = x+j, y+i {
						if m[y][x] == '#' {
							c++
						}
					}
					if c%2 == 1 {
						isPw = false
						break
					}
				}
			}
			if isPh && isPw {
				fmt.Println("YES")
				return
			}
		}
	}
	fmt.Println("NO")
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}