∵MH//C1D1
∴A1M:A1H=A1C1:A1D1
而对于正方体ABCD-A1B1C1D1,A1C1=AD1、AA1//DD1
又A1M=AN
故AN:A1H=AD1:A1D1
即HN//A1A
于是HM//D1C1、HN//D1D
所以面HMN//面D1C1CD
∵MH//C1D1
∴A1M:A1H=A1C1:A1D1
而对于正方体ABCD-A1B1C1D1,A1C1=AD1、AA1//DD1
又A1M=AN
故AN:A1H=AD1:A1D1
即HN//A1A
于是HM//D1C1、HN//D1D
所以面HMN//面D1C1CD