20.4 Complete the tree induction program of this section and test it on some learning problem, for example the one in Figure 20.9. Note that the procedure choose_attribute, using setof, is very inefficient and can be improved. Also add a procedure show( Decision Tree) for displaying decision trees in a readable form. For the tree in Figure 20.13, a suitable form is: holes none size small>screw large ==> pen 1 shape 2 long ==> key compact > nut other > null size small ==> key large ==>scissors 3=> null many ==> null