Just three lines.
This is the third.
Three lines is all that A or Z are, differing arrangements of three straight lines. All the components are the same; short horizontals and longer slanting strokes. All that makes each each is the particular way that the constituent parts are hung together, the recipe of logic with which each is baked; fundamentally no different than their cuneiform ancestors.
Three lines, two of one kind and one of another.
A - two slanted lines and a horizontal line.
Z – two horizontal lines and a slanted line.
There are many, many, many other possible arrangements that three such elements could make. However, it is into these two particular arrangements, that we have poured so much meaning. And, it is between A and Z, in the other linear arrangements situated there, that we have decided the rest of meaning resides.