# まず黒マスは偶数個である必要
# どの黒マスとどの黒マスをペアにするか、そのペア間の(i, j)距離
# その距離で全部の黒マスをペアリングできるか

H, W = map(int, input().split())
S = []
for i in range(H):
    S.append(input())
    
blacks = []
count = 0
count_matrix = [[-1]*W for h in range(H)]
for i in range(H):
    for j in range(W):
        if S[i][j] == '#':
            blacks.append((count, (i, j)))
            count_matrix[i][j] = count
            count += 1
            
black_total = count
ans = 'NO'
didj_visited = set()
if black_total%2 == 0:
    for a in range(black_total):
        for b in range(a+1, black_total):
            di = blacks[b][1][0]-blacks[a][1][0]
            dj = blacks[b][1][1]-blacks[a][1][1]
            if (di, dj) in didj_visited:
                continue
            didj_visited.add((di, dj))
            
            test = True
            visited = set()
            for c in range(black_total):
                if blacks[c][0] in visited:
                    continue
                visited.add(blacks[c][0])
                if not (0 <= blacks[c][1][0]+di < H and 0 <= blacks[c][1][1]+dj < W):
                    test = False
                    break                
                nxt_num = count_matrix[blacks[c][1][0]+di][blacks[c][1][1]+dj]
                if nxt_num in visited or nxt_num == -1:
                    test = False
                    break
                else:
                    visited.add(nxt_num)
            if test == True and len(visited) == black_total:
                ans = 'YES'
                #print(blacks[a], blacks[b], di, dj)
print(ans)