def read_data():
    H, W = map(int, input().split())
    S = [input() for i in range(H)]
    return H, W, S

def solve(H, W, S):
    Smat = [[c == '#' for c in row] for row in S]
    if has_no_sharp(Smat):
        return False
    for h in range(H):
        for w in range(W):
            if h == w == 0:
                continue
            if can_be_painted(h, w, Smat, H, W):
                return True
    return False

def has_no_sharp(Smat):
    for row in Smat:
        if any(row):
            return False
    return True

def can_be_painted(h, w, Smat, H, W):
    Scopy = [row[:] for row in Smat]
    for x in range(H):
        for y in range(W):
            if Scopy[x][y]:
                if x+h >= H or y+w >= W or not Scopy[x+h][y+w]:
                    return False
                else:
                    Scopy[x+h][y+w] = False
    return True

H, W, S = read_data()
if solve(H, W, S):
    print("YES")
else:
    Sreverse = [list(reversed(row)) for row in S]
    if solve(H, W, Sreverse):
        print("YES")
    else:
        print("NO")