[source: Swan 1995]
8. say so & tell sb so, instead of repeating information
e.g. Mary and John are getting married. Peter told me so.
9. I told you so = I warned you, but you did not heed my warning.
e.g. You’ve twisted your ankle. You shouldn’t jump off walls. I told you so.
10. so + hope, believe, understand, &c.
e.g. A: Is inflation going to come down? B: Oh, I hope so.
e.g. A: John and Peter are getting married. B: So I heard.