%% I am going to comment on one sample carefully and thoroughly I hope.
%% I hope any reader can learn enough to apply principles in other cases.

%% predicate1(Arg1, Arg2, Arg3) :- predicate2(Arg1, Arg2),
%%                                 predicate3(Arg1, Arg3).'

%% means if predicate3(Arg1, Arg2) and predicate3(Arg1, Arg3)
%%       then predicate1(Arg1, Arg2, Arg3).

%% ":-" means "if"
%% "," separates Arguments in predicates and means "and" between clauses.
%%

%% Two rules can be used for "or"
%% if we add
%% predicate1(Arg1, Arg2, Arg3) :- predicate4(Arg1, Arg2),
%%                                 predicate5(Arg1, Arg3).
%% then we have:

%%       if (predicate3(Arg1, Arg2) and predicate3(Arg1, Arg3))
%%       or (predicate4(Arg1, Arg2) and predicate5(Arg1, Arg3))
%%       then predicate1(Arg1, Arg2, Arg3).

%%   "\+" is negation by "failure" (if it cannot see it is true is says false)
%%   I also use qqqq4 to state positive facts in the database.
%%          and qqqq5 to state negative facts in the database.

%%   You can run WildLife on an totally empty file.
%%   It will produce no output - not even any errors!

%%   match_word below is recursive. Each call removes a Word.
%%   It also subtracts one from the Arity of the Relation_Idea.
%%   The list is finite in WildLIFE, so eventually there will be
%%   an empty list and the Arity can be checked. (or be -999)
%%   It also checks if the Ideas are one less in type than the Relation Idea.
%%   rrrr sees if the Subject has that relation between the Word and the Idea.

understands_words(Subject, Time, [[Relation_Word] | List]) :-
	rrrr(Subject, Time, Relation_Word, Relation_Idea),
	arity_idea(Relation_Idea, Arity),
	type_idea(Relation_Idea, Type),
	% List of Words.
	% Objects should be Type one less than Type of Relation
	match_word(Subject, Time, List, Arity, Type - 1).

%% The following are auxilary predicates - they have no ontological
%% Significance.

match_word(Subject, Time, [], 0, Type).

%% -999 indicates arbitrary arity.
match_word(Subject, Time, [], -999, Type).

match_word(Subject, Time, [[Word] | List],
	   Arity, Type) :-
	% List of Word Object Pairs.
	rrrr(Subject, Time, Word, Idea),
	type_idea(Idea, Type),
	match_word(Subject, Time, List,
		   % if Arity is not Arbitrary sub 1
		   cond(Arity =\= -999, Arity - 1, -999),
		   Type).