% AILog representation of binary trees with labeled leaves and internal nodes.

% This is the code discussed in Section 12.3.3 of Poole and Mackworth, Artificial
% Intelligence: foundations of computational agents, Cambridge, 2010.

% Copyright (c) David Poole and Alan Mackworth 2009. This program
% is released under GPL, version 3 or later; see http://www.gnu.org/licenses/gpl.html

% To run this in AILog, you should put it in the same directory as AILog and then call
% load 'trees.ail'.

% at_leaf(L,T) is true if label L is the label of a leaf in tree T.
at_leaf(L,leaf(L)).
at_leaf(L,node(N,LT,RT)) <-
    at_leaf(L,LT).
at_leaf(L,node(N,LT,RT)) <-
    at_leaf(L,RT).

% in_tree(L,T)  is true if label L is the label of an interior node of tree T
in_tree(L,node(L,LT,RT)).
in_tree(L,node(N,LT,RT)) <-
    in_tree(L,LT).
in_tree(L,node(N,LT,RT)) <-
    in_tree(L,RT).

% some example trees:
% Figure 7.4 (a):
tree1( node(length,leaf(skips),node(thread,leaf(reads),node(author,leaf(skips),leaf(reads)))) ).
% Figure 7.4 (b):
tree2( node(length,leaf(1.0),leaf(0.82)) ).

% Some queries:
% ask tree1(T) & at_leaf(L,T).
% ask tree1(T) & in_tree(L,T).
% ask tree2(T) & at_leaf(L,T).
% ask tree2(T) & in_tree(L,T).