I am reading a book about idiomatic expressions in Spanish. I just found something the I cannot believe. It says that "a + infinitive" can mean "if". The example is as follows: A haberlo comprado yo, yo lo hubiera devuelto. If I had bought it, I would have returned it. This sentence sounds natural to me, but I have still never heard of "a + infinitive" meaning "if". Gracias de antemano a cualquiera persona que me ayude.