Extensions to core Prolog.			{#extensions}
=========================

YAP includes a number of extensions over the original Prolog
language. Next, we discuss how to use the most important ones.

	+ @ref Rational_Trees

	+ @ref AttributedVariables

	+ @ref  DepthLimited

	+ @ref  Tabling

	+ @ref Threads

	+ @ref Profiling

	+ @ref YAPArrays

	+ @ref Parallelism

In the description of the arguments of predicates the following
notation will be used:
	
	+ a preceding plus sign will denote an argument as an "input
argument": the argument is read, not written, and it cannot be a free
variable at the time of the call.
	
	+ a preceding minus sign will denote an "output argument";

	+ an argument with no preceding symbol can be used in both ways.