propositions and logical operations on them became the principal subject of algebra of logic. Propositions are understood to mean statements about which it is meaningful to ask whether they are true or false. For instance, the proposition "a whale is an animal" is true, while the statement "all angles are right angles" is false. The connectives "and" , "or" , "if … then" , "is equivalent to" , the particle "not" , etc., which are commonly used in the language of logic, make it possible to construct new, more "complicated" , propositions from those already established. Thus, given that "x> 2" and "x≤ 3" , it is possible to obtain, by using the connective "and" , the proposition "x> 2 and x≤ 3" ; by using the connective "or" it is possible to obtain the proposition "x> 2 or x≤ 3" , etc.