irb(main):001:0> a = [3,1,4,1,5,9] => [3, 1, 4, 1, 5, 9] irb(main):002:0> a.length
irb(main):003:0> a[0] = a[4] => 5 irb(main):004:0> a[0]+a[2]
d=[[[0,0,0],[0,1,0],[0,0,1]], [[1,0,0],[1,1,0],[1,0,1]]] show(d)