Use 4 HALF-ADDERs to build a circuit that takes as input a 4-bit number
x and on its 4-bit output computes the twos-complement of x.

**Hint: first use a layer of INVERTERS to invert the input of x to produce the ones complement of
x, and then add to this the value 1 to produce the two’s complement.**

An 8-bit addition/subtraction unit with two's complement arithmetic and an accumulator.

BCD displays are added for nicer user experience.

First steps in CircuitVerse