x = a 	x = b 	x = c 	x = d

y = a 		1/8  |	1/16 |	1/16  |	1/4	
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y = b 		1/16 |	1/8  |	1/16  |	0
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y = c 		1/32 | 	1/32 |	1/16  |	0
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y = d 		1/32 |	1/32 |	1/16  |	0