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A truth table is a mathematical table used in logic—specifically in connection with Boolean algebra, Boolean functions, and propositional calculus—which sets out the functional values of logical expressions on each of their functional arguments, that is, for each combination of values taken by their logical variables. [1]
As an efficient procedure, however, truth tables are constrained by the fact that the number of valuations that must be checked increases as 2 k, where k is the number of variables in the formula. This exponential growth in the computation length renders the truth table method useless for formulas with thousands of propositional variables, as ...
The class of classical logic connectives (e.g. &, →) used in the construction of formulas is truth-functional. Their values for various truth-values as argument are usually given by truth tables. Truth-functional propositional calculus is a formal system whose formulae may be interpreted as either true or false.
In the abstract (ideal) case the simplest oscillating formula is a NOT fed back to itself: ~(~(p=q)) = q. Analysis of an abstract (ideal) propositional formula in a truth-table reveals an inconsistency for both p=1 and p=0 cases: When p=1, q=0, this cannot be because p=q; ditto for when p=0 and q=1.
Marquand diagram: truth table values arranged in a two-dimensional grid (used in a Karnaugh map) Binary decision diagram, listing the truth table values at the bottom of a binary tree; Venn diagram, depicting the truth table values as a colouring of regions of the plane; Algebraically, as a propositional formula using rudimentary Boolean functions:
A truth table is a semantic proof method used to determine the truth value of a propositional logic expression in every possible scenario. [92] By exhaustively listing the truth values of its constituent atoms, a truth table can show whether a proposition is true, false, tautological, or contradictory. [93] See § Semantic proof via truth tables.
The truth or falsehood of a proposition is called its truth value. A formula, or set of formulas, is said to be satisfiable if there is a possible assignment of truth-values to the propositional letters such that the entire formula, which combines the letters with connectives, is itself true as well. [1]
An XNOR gate can be implemented using a NAND gate and an OR-AND-Invert gate, as shown in the following picture. [3] This is based on the identity ¯ (¯) ¯ An alternative, which is useful when inverted inputs are also available (for example from a flip-flop), uses a 2-2 AND-OR-Invert gate, shown on below on the right.