CS 342 Lecture -*- Outline -*-

* reachability problem for positive 2-dimensional vector systems
	advert: slick use of lazy evaluation for modularity
		distinction between breadth-first and depth first search
			that is similar to what will be important in Prolog

** the problem
	add up vectors to get a particular vector:
		draw picture instead of the following:

		let B = {b_i} be a set of integer vectors b_i = (k,l)
		let Span(B) = { path(B) | path(B) = sum_i of a_i*b_i,
						where a_i is an integer}
		problem: is p in Span(B)?

	explain gen-paths, starting with the last line.
		note that genpaths constructs an infinite tree,
			which is a list of nested lists

	note dfs* and dfs are mutually recursive

	but bsf-queue is just auxilliary function for bfs