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In logic and mathematics, statements and are said to be logically equivalent if they have the same truth value in every model. [1] The logical equivalence of p {\displaystyle p} and q {\displaystyle q} is sometimes expressed as p ≡ q {\displaystyle p\equiv q} , p :: q {\displaystyle p::q} , E p q {\displaystyle {\textsf {E}}pq} , or p q ...
The corresponding logical symbols are "", "", [6] and , [10] and sometimes "iff".These are usually treated as equivalent. However, some texts of mathematical logic (particularly those on first-order logic, rather than propositional logic) make a distinction between these, in which the first, ↔, is used as a symbol in logic formulas, while ⇔ is used in reasoning about those logic formulas ...
Note that P ∨ Q ∨ R is logically equivalent to (¬P ∧ ¬Q) → R. In English, this first-order sentence reads: Given any set X, X contains the empty set as an element or the elements of X are not pairwise disjoint or there exists a set C such that its intersection with any of the elements of X contains exactly one element.
The negation is "There exists a red object that does not have color." This statement is false because the initial statement which it negates is true. In other words, the contrapositive is logically equivalent to a given conditional statement, though not sufficient for a biconditional.
compound statement A statement in logic that is formed by combining two or more statements with logical connectives, allowing for the construction of more complex statements from simpler ones. [67] [68] comprehension schema A principle in set theory and logic allowing for the formation of sets based on a defining property or condition.
In propositional logic, material implication [1] [2] is a valid rule of replacement that allows a conditional statement to be replaced by a disjunction in which the antecedent is negated. The rule states that P implies Q is logically equivalent to not- P {\displaystyle P} or Q {\displaystyle Q} and that either form can replace the other in ...
In mathematics, a characterization of an object is a set of conditions that, while possibly different from the definition of the object, is logically equivalent to it. [1] To say that "Property P characterizes object X" is to say that not only does X have property P, but that X is the only thing that has property P (i.e., P is a defining ...
This is a statement in the metalanguage, not the object language. The notation a ≡ b {\displaystyle a\equiv b} may occasionally be seen in physics, meaning the same as a := b {\displaystyle a:=b} .