The house had two entrances

You have one tetrahedron which is the gate that's going to do your computing, and you have two input tetrahedrons.

And then finally the last two entries are going to be the top row of A, 1, minus 1, 2, dotted with this column vector, 1, minus 1, 2 a little dot there, remember we're taking the dot product and then finally this second row of A, so 0, minus 2, 1, dotted with this column vector, 1, minus 1, 2.

In the long term, expanding technical cooperation among countries in transition and overcoming barriers to their growth could provide additional inputs for the same purpose, albeit indirectly.