Question text is in black, answers in blue.
To draw a Hasse diagram you need a finite partial order, which is some
finite set A
and a binary relation P on A that is reflexive, antisymmetric, and
transitive. For the first part of 2.10.4(c), your set A is the set
of all strings that are substrings of "abbac", according to the
definition of "substring" in the book. This set A is finite because
only some strings are substrings of "abbac". Your relation P(u,v)
is given by "u is a substring of v" -- in 2.10.4(a) you proved that
this is a partial order. Since λ is a substring of every
string in A, it will be at the bottom of your Hasse diagram. Since
every string in A is a substring of "abbac", that string will be at
the top.
Once you have done this for "abbac", you repeat for the set of
substrings of "cababa".
Last modified 20 February 2011