Add new BDD example: TAOCP exercise 43.

[msk-ono]

• [ ] : $f(x1, \dots, x{2n}) = [x_1 + \dots + xn = x{n+1} + \dots + x_{2n}]$
• [ ] : $f(x1, \dots, x{2n}) = [x_1 + x3 + \dots + x{2n-1} = x_2 + x4 + \dots + x{2n}]$