Baby monads
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-Read the material on dividing by zero/towards monads from the end of lecture
-notes for week 6, then write a function `lift'` that generalized the
+Read the material on dividing by zero/towards monads from <strike>the end of lecture
+notes for week 6</strike> the start of lecture notes for week 7, then write a function `lift'` that generalized the
correspondence between + and `add'`: that is, `lift'` takes any two-place
operation on integers and returns a version that takes arguments of type `int
option` instead, returning a result of `int option`. In other words, `lift'`