==> geometry/touching.blocks.s <== n=0: 6 separate blocks n=1: 3 pairs n=2: 2 threesomes n=3: a 3x3 grid n=4: a box (each sides touches the four adjoining sides, but not the opposite) n=5: Crude ascii: Front view: Side view: /\ /\ ----- / \/ \ | | | / /\ \ | | | / / \ \ | | | \ /----\ / ---|.|.|--- \/| |\/ | | | | | ----------- ----------- | | | | ----------- ----- -- stein.kulseth@tf.tele.no [X.400] stein.kulseth@nta.no [internet] Place block A onto the x-y plane so that four of its corners are at (0,0), (0,1), (4,0), (4,1) (I give x and y coordinates only because the z coordinate will always be obvious). Place block B so four of its corners are at (2,1), (2,2), (6,1), (6,2). Now place block C with one 4x1 face on the x-y plane with one corner at (0,1) (tangent to block A) and tangent to block B at (2,1). Note that the angle between block A and block C is arctan(1/2), and a corner of block C will be at a point with approximate coordinates (3.5777, 2.7888). Call this point P. Now place an identical configuration of blocks on top of the first three as follows: block D with corners at (3.4,0.4), (4.4,0.4), (3.4,4.4), (4.4,4.4), block E with corners at (2.4,2.4), (3.4,2.4), (2.4,-1.6), (3.4,-1.6), and block F with one corner tangent to D at (3.4,4.4) and one side tangent to E at (2.4,2.4). If you have been plotting this on graph paper, then the following will be clear: Every block touches every other in its own layer. And A and B each touch D and E, and block C touches F. Point P falls under block D, so blocks C and D touch, and by symmetry so do blocks F and A. And the edge of block C intersects the edge of block E at (2.4,2.2) so blocks C and E touch, and by symmetry so do blocks F and B. Done! -- David Karr (karr@cs.cornell.edu) All the blocks are placed with their 2x4 face UP, although any face up would have worked, as it turns out. The blocks are called AAAA BBBB CCCC, etc. AAAA AAAA /_______ BBCC \ BBCC BBCC BBCC /\ || The two arrows point to the intersection of AC and BC. Now take block "D" and place the top edge along the diagonal (between the two arrows) so that the block extends SOUTH EAST of the line. Likely now the block does not touch either A or B. So slide the block towards the NORTH WEST so that it just touches A and B. You can now easily place blocks E and F perpendicular to block "D" so that they both touch all of ABC.....QED -- Guy Cousineau