Answer Introduce a do block with rule 3.

main =
  do
     (getLine >>= putStrLn) >>
       (getLine >>= putStrLn)

Then use rule 1.

main =
  do
     (getLine >>= putStrLn) 
     (getLine >>= putStrLn)

Finally apply rule 2 twice.

main = 
  do line1 <- getLine
     putStrLn line1
     line2 <- getLine
     putStrLn line2

Which is the example we started this section with.