H,W = list(map(int, input().split(' ')))

blacks = {}
for h in range(H):
    boxes = input()
    for w in range(W):
        if boxes[w] == '#':
            blacks[(h,w)] = 0

if len(blacks) == 0 or len(blacks) % 2 != 0:
    print('NO')
    exit()

def check(i, j):
    yes = True
    for key in blacks.keys():
        blacks[key] = 0
    for (h,w) in sorted(blacks.keys()):
        if blacks[(h,w)] == 0:
            blacks[(h,w)] = 1
            if (h+i,w+j) not in blacks:
                yes = False
                break
            else:
                blacks[(h+i,w+j)] = 1
    if yes:
        print('YES')
        exit()    
    
# check from top to bottom
for i in range(1,H):
    check(i, 0)

# check from left to right
for j in range(1,W):
    check(0, j)

# check from upper left to lower right
for i in range(1,H):
    for j in range(1,W):
        check(i, j)

# check from upper right to lower left
for i in range(1,H):
    for j in range(1,W):
        check(i, -j)        

print('NO')