Is the example given on the bottom right of p. 4 of the rules a valid or invalid tile setup? According to the rule above on the page 'you must place tiles so that open edges are adjacent to other open edges', how is this example valid or invalid? Looking at the tiles and the way this is worded... it doesn't make sense to me. When it says, 'a wall can never be placed against an open edge'. What does 'against' mean? Along the side of, adjacent to?