import sys


def input(): return sys.stdin.readline().rstrip('\n')


def ok(s, dh, dw):
    h, w = len(s), len(s[0])

    s = [list(r) for r in s]

    for i in range(h):
        for j in range(w):
            if s[i][j] == '#':
                if i+dh >= h or not (0 <= j+dw < w) or s[i+dh][j+dw] == '.':
                    return False
                s[i][j] = s[i+dh][j+dw] = '.'
    return True


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

    if all('#' not in r for r in s):
        print('NO')
        return

    for dh in range(h):
        for dw in range(-w+1, w):
            if (dh, dw) <= (0, 0):
                continue
            if ok(s, dh, dw):
                print('YES')
                return
    print('NO')


if __name__ == '__main__':
    main()