The author, in an adorable little attempt to wear big-boy pants[0], seems not to know that '<' is a message passed to a receiver. You can even redefine it if you like.

Better pseudo code would be

    1.lt(2).lt(3)

In fact, this is correct (albeit ungainly) ruby code

    1.<(2)  # true

and so

    1.<(2).<(3) # Say wha ... ?

makes no sense.

[0]: Yes, a cheap shot.