def check(a,b):
    valid = [vi[:] for vi in V]
    for i in range(h):
        for j in range(w):
            if valid[i][j]:
                if i+a >= h or j+b >= w or valid[i+a][j+b]==0:
                    return 0
                else:
                    valid[i+a][j+b] = 0
    return 1
    
h,w = map(int,input().split())
b = [input() for _ in range(h)]
V = [[1 if b[i][j]== "#" else 0 for j in range(w)] for i in range(h)]

ok = 0
for i in range(h):
    for j in range(w):
        if i==j==0: continue
        if check(i,j):
            ok = 1
            break
    if ok: break

for i in range(h): V[i] = V[i][::-1]
for i in range(h):
    for j in range(w):
        if i==j==0: continue
        if check(i,j):
            ok = 1
            break
    if ok: break

any1 = max(max(vi) for vi in V)
print("YES" if ok and any1 else "NO")