I encountered a text which says that the leakage current Ico (or called Icbo) adds up to the signal current hence causes thermal runaway because it causes temperature to increase and it also increases with temperature. Below is the related illustration circuit(I guess we are not in control of Vbe anymore):
As a remedy the text shows these alternatives:
What I understand from above alternatives is that it seems if we are in total control of Vbe(by using a voltage source at BE terminals), then the Ico will not affect the biasing circuit.
If my understanding is correct, how does the circuit on the right(with voltage divider) is equivalent to the circuit on the left(with voltage source)? How is this source transformation done in electric circuit theory? Somehow the author equalizes the voltage source to a voltage divider but how?