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

X = []
Y = []
dic = {}
for i in range(h):
    for j in range(w):
        if S[i][j] == "#":
            dic[i * 100 + j] = len(X)
            X.append(i)
            Y.append(j)
            
l = len(X)
if l % 2 == 1:
    print("NO")
    exit()
    
i = 0
for j in range(i + 1, l):
    di = X[j] - X[i]
    dj = Y[j] - Y[i]
    used = [False] * l
    for k in range(l):
        if used[k]:
            continue
        ni = X[k] + di
        nj = Y[k] + dj
        if ni * 100 + nj not in dic:
            break
        x = dic[ni * 100 + nj]
        used[x] = True
    else:
        print("YES")
        exit()
print("NO")