H, W = map(int, input().split())
G = []
flag = 1
sx, sy = 0, 0
for i in range(H):
    G.append(list(input()))
    if flag:
        for j in range(W):
            if G[i][j] == "#":
                sx = i
                sy = j
                flag = 0
                break

s = (sx, sy)
for gx in range(H):
    for gy in range(W):
        g = (gx, gy)
        if G[gx][gy] != "#" or s == g:
            continue
        S = set()
        S.add(s)
        S.add(g)
        dx = g[0] - s[0]
        dy = g[1] - s[1]
        flag = 1
        for i in range(H):
            for j in range(W):
                if G[i][j] != "#":
                    continue
                if (i, j) in S:
                    continue
                nx = i + dx
                ny = j + dy
                if (nx, ny) in S:
                    continue
                if nx < 0 or nx > H - 1 or ny < 0 or ny > W - 1:
                    flag = 0
                    break
                if G[nx][ny] != "#":
                    flag = 0
                    break
                S.add((nx, ny))
        if flag:
            print("YES")
            exit()
print("NO")