def res():
    import copy

    H,W=map(int,input().split())
    S=[[None] for _ in range(H)]

    for i in range(H):
        S[i]=list(input())

    b=[]
    for i in range(H):
        for j in range(W):
            if S[i][j]=='#':
                b.append([i,j])

    if (len(b)>1)and(len(b)%2==0):
        o=b[0]
        for i in b:
            if i==b[0]:
                continue
            l1=i[0]-o[0]
            l2=i[1]-o[1]
            t=copy.deepcopy(S)
            for j in b:
                if t[j[0]][j[1]]=='B':
                    if j==b[-1]:
                        return 'YES'
                    continue
                if (0<=(j[0]+l1)<H)and(0<=(j[1]+l2)<W):
                    if t[j[0]+l1][(j[1]+l2)]=='#':
                        t[j[0]+l1][(j[1]+l2)]='B'
                    else:
                        break
                else:
                    break
        return 'NO'
    return 'NO'

print(res())