H, W = map(int, input().split())
c = []
cnt = 0
for _ in range(H):
    s = list(input())
    cnt += s.count('#')
    c.append(s)
if cnt == 0 or cnt%2==1:
    print('NO')
    exit()

def solve(i, j):
    r1, r2 = range(H), range(W)
    r11, r22 = reversed(range(H)), reversed(range(W))
    w1 = [r1, r11]
    w2 = [r2, r22]
    p, q = w1[i<0], w2[j<0]
    b = set()
    for x in p:
        for y in q:
            if x+i<0 or x+i>H-1 or y+j<0 or y+j>W-1:
                if (x, y) not in b and c[x][y]=='#':
                    return False
                else:
                    continue
            if (x, y) in b or c[x][y] == '.':
                continue
            b.add((x, y))
            if c[x+i][y+j]=='.':
                return False
            else:
                b.add((x+i, y+j))
    return True

for i in range(-H+1, H):
    for j in range(-W+1, W):
        if i == j:
            continue
        if solve(i, j):
            print('YES')
            exit()
print('NO')