from copy import deepcopy
def Check1(N, M, A):
    def dfs(x, y, rx, ry):
        for i in range(4):
            nx = x + dx[i]
            my = y + dy[i]
            if nx < 0 or N <= nx or my < 0 or M <= my:
                continue
            if nx == rx and my == ry:
                continue
            if L[nx][my] == '#':
                continue
            L[nx][my] = '#'
            dfs(nx, my, x, y)
    L = deepcopy(A)
    flg = False
    for i in range(N):
        for j in range(M):
            if L[i][j] == '.':
                if flg:
                    print('NO')
                    exit()
                dfs(i, j, -1, -1)
                flg = True

def Check2(N, M, A):
    def Count(x, y):
        ret = 0
        for i in range(4):
            nx = x + dx[i]
            my = y + dy[i]
            if nx < 0 or N <= nx or my < 0 or M <= my:
                continue
            if A[nx][my] == '.':
                ret += 1
        return ret
    cnt = [[0] * M for _ in range(N)]
    for i in range(N):
        for j in range(M):
            if A[i][j] == '.':
                cnt[i][j] = Count(i, j)
                if cnt[i][j] == 1:
                    print('NO')
                    exit()
                cnt[i][j] -= 2
    return cnt

def Check3(N, M, cnt):
    def dfs(x, y, rx, ry):
        for i in range(4):
            nx = x + dx[i]
            my = y + dy[i]
            if nx < 0 or N <= nx or my < 0 or M <= my:
                continue
            if nx == rx and my == ry:
                continue
            if L[nx][my] == 0:
                continue
            L[nx][my] = 0
            dfs(nx, my, x, y)
    L = deepcopy(cnt)
    flg = False
    for i in range(N):
        for j in range(M):
            if L[i][j] > 0:
                if flg:
                    print('NO')
                    exit()
                dfs(i, j, -1, -1)
                flg = True

def Check4(N, M, cnt):
    flg = False
    for i in range(N):
        for j in range(M):
            if cnt[i][j] == 2:
                if flg:
                    print('NO')
                    exit()
                flg = True

def Check5(N, M, cnt):
    def dfs(x, y):
        ret = 0
        for i in range(4):
            nx = x + dx[i]
            my = y + dy[i]
            if nx < 0 or N <= nx or my < 0 or M <= my:
                continue
            ret += cnt[nx][my]
        return ret
    for i in range(N):
        for j in range(M):
            if cnt[i][j] == 2:
                if dfs(i, j) == 4:
                    print('NO')
                    exit()

N,M = map(int,input().split())
A = [list(input()) for _ in range(N)]
if N == 1 or M == 1:
    print('NO')
    exit()
dx = [0, 0, 1, -1]
dy = [1, -1, 0, 0]
Check1(N, M, A)
cnt = Check2(N, M, A)
Check3(N, M, cnt)
Check4(N, M, cnt)
Check5(N, M, cnt)
print('YES')