For example, in an "imperative" programming setting, formula_1 would mean that formula_2 is being assigned the result of formula_3 in the instant the expression is evaluated, and later, the values of formula_4 and formula_5 can be changed with no effect on the value of formula_2. On the other hand, in "reactive" programming, the value of formula_2 is automatically updated whenever the values of formula_4 or formula_5 change, without the program having to explicit re-execute the statement formula_1 to determine the presently assigned value of formula_11