surah

Reciting a surah or aayaat equivalent to a surah in Salaah

Q: I believe that in a book I read titled, Laws of salah, written by Muhammad Ilyas Attar Qadari Razavi (Dawat-e-Islami) it said on the hundred and fifth page these following words:-

'After you finish surah Fatihah, utter amin in a low volume and then recite either three short ayahs or one long ayah that is equivalent to three short ayahs or any surah such as surah Ikhlas.'

I had a query based on the last line of this paragraph. When it quotes, 'or any surah,' do you think that this is implying that after surah Fatihah has been recited you can recite another surah, or is it suggesting that after surah fatihah you can recite an ayah that is equivalent to another surah, or do you think that it can be referring to both?

Forgetting to recite a Surah in the third rakaat of Sunnat Salaah

Q: I performed the four sunnah of Asr salaah however in the 3rd rakaat I forgot to read a Surah after Surah Fatiha only realised this in ruku. I intended to make sajda sahwa but after the 4th rakaat I read the tashahud, durood and dua and made both salaams. Whilst making the second salaam I remembered the sajda-e-sahw and immediately made a sajda after then completed the Salaah. Was I correct or did I have to repeat the Salaah?