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

points = []
dic = {}
for i in range(h):
    for j in range(w):
        if S[i][j] == "#":
            dic[(i, j)] = len(points)
            points.append((i, j))
            
l = len(points)
if l % 2 == 1:
    print("NO")
    exit()
    
for i in range(l):
    for j in range(i + 1, l):
        di = points[j][0] - points[i][0]
        dj = points[j][1] - points[i][1]
        used = [False] * l
        for k in range(l):
            if used[k]:
                continue
            ni = points[k][0] + di
            nj = points[k][1] + dj
            if (ni, nj) not in dic:
                break
            x = dic[(ni, nj)]
            used[x] = True
        else:
            print("YES")
            exit()
print("NO")