Embodiments relate to the emulation of circuits, and representation of unknown states of signals. A disclosed system (and method and computer program product) includes an emulation environment to convert a digital signal of a DUT in a form capable of representing an unknown state. In addition, the disclosed system converts digital logic circuits such as Boolean logic, flip flops, latches, and memory circuits to be operable with signals having unknown states. Thus, an unknown state of a signal is indicated and propagated through digital logic circuits represented in a disclosed semantic to enable prompt detection of improper operation of the DUT, for example, due to power shut down or inadequate initialization.