import sys


def input():
    return sys.stdin.readline().strip()


def main():
    h, w = map(int, input().split())
    s = [input() for _ in range(h)]

    for dh in range(h):
        for dw in range(w):
            fail = False
            filled = [[0]*w for _ in range(h)]
            for i in range(h):
                for j in range(w):
                    if not (s[i][j] == "#" and not filled[i][j]):
                        continue
                    filled[i][j] = True

                    ii, jj = i+dh, j+dw
                    if ii < h and jj < w and s[ii][jj] == "#" and not filled[ii][jj]:
                        filled[ii][jj] = True
                    else:
                        fail = True
                        break
                if fail:
                    break
            else:
                return "YES"

    return "NO"


print(main())