17. Step 0 of 144
This rule also succeeds
Step 22 of 144
18. This is a partial solution
If X is orville, any Y such that
father(abe, Y) will be a solution
father(Z, Y) is the is new goal. After the
substitution (X = oriville, Z = abe), it
becomes father(abe, Y)
Step 23 of 144