Denote a definition by :=, not ≡

Defining A to be B is an operation asymmetric between the two sides: it takes whatever value that B has and assigns it to A. If A does not have a value beforehand, the operation fills the void; else the operation replaces the previous value of A with the one taken from B. Such asymmetry is captured by the symbol := or the pseudocode <--- in algorithm theory. By contrast, ≡ or =, albeit widely used in economics literature to denote definitions, is a symbol symmetric to both sides. Unless we add an asymmetric connotation to ≡ (but then why not simply use :=?), "A≡B" would be a statement asserting equivalence between A and B, meaningless if A has not been assigned a value. By contrast, "A:=B" is an operation that can be carried out as long as B has been assigned a value, whether A has a value or not. With :=, we can express recursive operations such as "incrementing the variable x by one" as x:=x+1, while "x≡x+1" makes no sense.