import copy
H,W = map(int,input().split())
S = [list(input()) for _ in range(H)]
A = []
for i in range(H):
    for j in range(W):
        if S[i][j]=="#":
            A.append((i,j))
si,sj = A[0]
for k in range(len(A)):
    flag = "YES"
    T = copy.deepcopy(S)
    y,x = A[k]
    di,dj = y-si,x-sj
    for m in range(len(A)):
        i,j = A[m]
        if T[i][j]=="#":
            T[i][j] = 0
            if 0<=i+di<H and 0<=j+dj<W and T[i+di][j+dj]=="#":
                T[i+di][j+dj] = 1
            else:
                flag = "NO"
                break
    if flag=="YES":break
print(flag)