Some examples of 2-cnf boolean expressions.  All variables have boolean type.
Don't forget that in the hierarchy of boolean operators, "not" has higher
precedence than "or."

1. (x or y) and (not x or z) and (y or not z)

2. (a or b) and (c or d) and (not a or c) and (not b or d) and (not c or not b)

3. (finished or ready) and (not ready or not ok) and (ready or done) and
  (ok or happy) and (finished or not happy) and (not ready or not done) and
  (ready or sad) and (happy or sad) and (ok or not sad)