OK, I was looking over some grammar exercises, and I saw "один" used in some ways I hadn't seen (or noticed perhaps). This brings me to my questions:
1. Он в киоске купил один конверт и одну марку. Is there ANY difference from just saying Он в киоске купил конверт и марку. I understand the meaning, but is there any context in which one is better/different from the other? Does one sound better to your native-Russian ears?
2. Is один 100% interchangable with только? Can I say Только Бог знает and have it mean exactly what Один Бог знает? На тарелке остались одни крошки is 100% interchangable with На тарелке остались только крошки?
3. And finally, is it interchangable with самый and тот же? Are all these acceptable and equal statements?:
- Мы учились в одной школе.
- Мы учились в той же школе.
- Мы учились в самой школе.