离散数学逻辑部分复习(一)：单词，及注解

glossary:
1. statement: a declarative sentence that is either true or false.
2. compound statements:statements or propositional variables can be combined by logical connectives to obtain compound statements.
3. negation if p is a statement , the negation of p is the statement not p , denoted by ¬ p.
4. conjunction :if p and q are statements , the conjunction of p and q is the compound statement “p and q”,denoted by p ⋀ q.
5. disjunction : if p and q are statements , the disjunction of p and q is the compound statement “p or q” , denoted by p ⋁ q.
6. predicate,propositional function
7. universal quantification : ∀
8. existential quantification: ∃
9. conditional statement : if p and q are statements , the compound statement “if p then q “, denoted by p ⇒ q, is called a conditional statement or implication. p is called antecedent or hypothesis , and the statement q is called the consequence or solution;
10. converse: q ⇒ p
11. contrapositive: ~q ⇒ ~p.
12. equivalence,biconditional : p ⇔ q.
13. contradiction:a statement that is always false.
14. tautology: a statement that is always true.
15. contingency:depending on its propositional variables . it can be true or false.
16. logically equivalent