import java.util.*;
import static java.lang.System.*;
import java.io.*;

public class Main {
	static FastScanner sc = new FastScanner(System.in);
	public static void main(String[] args) {
		int H = sc.nextInt();
		int W = sc.nextInt();
		LinkedList<Point> p = new LinkedList<Point>();
		String s;
		char c;
		for (int i=0; i<H; i++) {
			s = sc.next();
			for (int j=0; j<s.length(); j++) {
				c = s.charAt(j);
				if (c=='#') {p.add(new Point(i,j));}
			}
		}
		int size = p.size();
		if (size%2==1) {out.println("NO"); return;}
		
		//ここから平行移動処理
		LinkedList<Point> p2 = new LinkedList<Point>();
		int y,x;
		size = p.size()/2;
		for (int i=0; i<H; i++) {
			for (int j=1-W; j<W; j++) {
				p2 = (LinkedList<Point>)p.clone();
				for (int k=0; k<size; k++) {
					y = p2.getFirst().getY()+i;
					x = p2.removeFirst().getX()+j;
					for (int l=0; l<p2.size(); l++) {
						if (p2.get(l).getY()==y && p2.get(l).getX()==x) {
							p2.remove(l);
						}
					}
				}
				if (p2.size()==0) {out.println("YES"); return;}
			}
		}
		out.println("NO");
	}
}

class Point {
	private int y;
	private int x;
	public Point (int y, int x) {
		this.y = y;
		this.x = x;
	}
	public int getY () {
		return this.y;
	}
	public int getX () {
		return this.x;
	}
	public int setY (int y) {
		return this.y = y;
	}
	public int setX (int x) {
		return this.x = x;
	}
}



class FastScanner implements Closeable {
	private final InputStream in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;
	public FastScanner(InputStream in) {this.in = in;}
	private boolean hasNextByte() {
		if (ptr < buflen) {return true;}
		else{
			ptr = 0;
			try {buflen = in.read(buffer);}
			catch (IOException e) {e.printStackTrace();}
			if (buflen <= 0) {return false;}
		}
		return true;
	}
	private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
	public String next() {
		if (!hasNext()) throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public long nextLong() {
		if (!hasNext()) throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {throw new NumberFormatException();}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){return minus ? -n : n;}
			else{throw new NumberFormatException();}
			b = readByte();
		}
	}
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
		return (int) nl;
	}
	public double nextDouble() { return Double.parseDouble(next());}
	public void close() {
		try {in.close();}
		catch (IOException e) {}
	}
}