% debug(Root, Bug)
% Root is the root of a tree representing the buggy
% computation.  Bug is a buggy node in the tree.
%
debug(Root, Bug) :-
	erroneous(Root),
	(if some [Child, Bug1] (	% (
		child(Root, Child),	%	child(Root, Child),
		debug(Child, Bug1))	%	debug(Child, Bug1)
	then				% ->
		Bug = Bug1		%	Bug = Bug1
	else				% ;
		Bug = Root		%	Bug = Root
	).				% ).

% erroneous(Node)
% Node is a node in the tree (a sub-computation) which has
% an incorrect result.
% (definition depends on what we are debugging and how
%  the computation is represented)

% child(PNode, CNode)
% CNode is a child (subcomputation) of node (computation) PNode
% (definition depends on what we are debugging and how
%  the computation is represented)