Identifying system from energy relationships

[From Bill Powers (931214.2130 MST)]

Martin Taylor (931214.1725) --

[Given energy relationships] you can at least determine what
kind of a heat engine you are dealing with, and with the
entropy relationships you may be able to determine whether it
is a control system and if so what the gain is.

All right. We have a power output O and two power inputs, I1 and
I2. The energy relationship is O = I1 + I2.

What kind of system are we talking about?

Best,

Bill P.