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))
if len(A)==0:
    flag = "NO"
else:
    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)