I have been reading the Digital Design: Principles and Practices 3rd Edition as a hobby. Unfortunately, I am stuck at page 103 of Section 3.5.2: Circuit Behavior with Resistive Loads.
In Figure 3-27: https://ibb.co/v1BVXrK, a resistive model of a CMOS inverter with a resistive load has been illustrated. (a) showing the actual load circuit and (b) using the Thevenin equivalent of the load.
To understand how Figure 3.27(a) is equivalent to Figure 3.27(b), I learned how the Thevenin theorem works. I watched a brilliant course about the theorem: https://www.youtube.com/watch?v=25axDabtoFk.
However, as far as I understand from the Thevenin theorem, we remove a circuit component and make it an open circuit. After the removal, we have only 2 open terminals. Whereas in Figure 3.27(a), by removing the components in the right-hand-side blue rectangle, we are making 3 open terminals, not 2.
So, how does the author convert Figure 3.27(a) to Figure 3.27(b) using the Thevenin theorem?