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The multiple-valued logics obtained by introducing uncertainty and energy considerations into classical switching theory are studied in this paper. First, the nature of uncertain or unknown signals is examined, and two general uncertainty types called U-values and P-values are identified. It is shown that multiple-valued logics composed of U/P-values can be systematically derived from 2-valued Boolean algebra. These are useful for timing and hazard analysis, and provide a rigorous framework for designing gate-level logic simulation programs. Next, signals of the form (v, s) are considered where v and s denote logic level and strength, respectively, and the product vs corresponds to energy flow or power. It is shown that these signals form a type of lattice called a pseudo-Boolean algebra. Such algebras characterize the behavior of digital circuits at a level (the switch level) intermediate between the conventional analog and logical levels. They provide the mathematical basis for an efficient new class of switch-level simulation programs used in MOS VLSI design.