h,w=map(int,input().split())
data=[]
for i in range(h):
    data+=input().split()
data=[c for l in data for c in l]
if '#' not in data:
    print('NO')
    exit()
for i in range(1,h*w):
    t=data[:]
    d=-1
    for j in range(len(t)):
        if t[j]=='#':
            if j+i<len(t) and t[j+i]=='#' and (d==(j+i)//w-(j)//w or d==-1):
                t[j],t[j+i]='.','.'
                d=(j+i)//w-(j)//w
            else:
                break
    else:
        print('YES')
        break
else:
    print('NO')