import sys
from itertools import product

H, W = map(int, input().split())
S = [input() for _ in range(H)]

def solve(h0, w0, dh, dw):
    color = [[None] * W for _ in range(H)]
    color[h0][w0] = 'R'
    color[h0 + dh][w0 + dw] = 'B'
    for h, w in product(range(h0, H), range(W)):
        if h == h0 and w <= w0: continue
        if S[h][w] == '#' and color[h][w] == None:
            if h + dh < H and w + dw < W and S[h + dh][
                    w + dw] == '#' and color[h + dh][w + dw] == None:
                color[h][w] = 'R'
                color[h + dh][w + dw] = 'B'
            else:
                return False
    for h, w in product(range(H), range(W)):
        if S[h][w] == '#' and color[h][w] == None:
            return False
    return True

h0 = w0 = -1
for h, w in product(range(H), range(W)):
    if S[h][w] == '#':
        h0, w0 = h, w
        break
else:
    print('NO')
    sys.exit()

yes = False

for h, w in product(range(h0, H), range(W)):
    if h == h0 and w <= w0: continue
    if S[h][w] == '#':
        dh, dw = h - h0, w - w0
        if (solve(h0, w0, dh, dw)):
            yes = True
            break

print('YES' if yes else 'NO')