Do exercise 19.3 on page 410.
Do exercise 19.6 on page 410.
Do exercise 19.8 on page 410.
Do exercise 19.9 on page 410.
Do exercise 19.14 on page 411.
Do exercise 20.1 on page 443. To make sure that your MGUs really are MGUs, remember that the MGU of two terms should unify those terms when applied to them in a single pass; it shouldn't be necessary to do substitutions and then further substitions in the result.
Do exercise 20.2 on page 443. (Because you are not to collect the substituted query term, the key thing to check is that you get the right number of solutions.)
Do exercise 20.3 on page 443.
Exercise 20.x1: Write a Prolog program so that the query p. initially produces the result true, but if the semicolon key is pressed so as to search for another solution, the program goes into an infinite loop. Draw a proof tree like those on page 428 to illustrate why your program behaves this way.