If x is y and y is z is x the same as z?

Well, 'x' is equal to 'z'.

Back in plane geometry, there was a mantra that said:

"Two quantities equal to the same quantity are equal to each other."

This question is an example of that mantra.

So for Example:

If x = 10

Then

x = y (making y = 10)

y = z (making z = 10)

therefore z is the same.