set inclusion of occurrences

	Hi -

	In the Formal Semantics, section 7.5.1, it contains a sentence:

		... where the "<=" operator for occurrence
		indicators denotes set inclusion of the subsets
		of the allowed occurrences.

	Can you please explain that in more detail?  Specifically, given
	the occurrence indicators:

		0 1 ? * +

	can you either specify a strict ordering of those or can you
	specify the table for "<=", i.e.:

		a | b | a <= b
		==============
		0 | 0 |
		0 | 1 |
		0 | ? |
		0 | * |
		0 | + |
		1 | 0 |
		1 | 1 |
		1 | ? |
		1 | * |
		1 | + |
		...
		+ | 0 |
		+ | 1 |
		+ | ? |
		+ | * |
		+ | + |

	?  Thanks.

	- Paul