For the given combination of values for the loose variables, an expression can be evaluated to a value, & is said to keep close at hand that value, although for a select few combinations of values of a loose variables, the expression can be vague. So an expression is the work of the values for the loose variables.

A evaluation of an expression is contingent on a definition of the mathematical operators & models of values that forms the context of an expression.

Both expressions come said to exist as equivalent if, for each combination of values for a loose variables, it use at times the equivalent value, we.e., it represent a equivalent work.

Case:

A expression has yours free! variable x, attached variable y, constants Ace, 2, & Trine, two occurrences of an inexplicit multiplication operator, & the summation operator. A expression is same by owning a simpler expression Dozenx. A value for x=Iii is 36.

Expressions & their evaluation were formalised by Alonzo Church and Stephen Kleene in the 1930s in their lambda calculus. the lambda calculus has been a major influence in the development of modern maths & computer programming languages.

One of a extra interesting effects of a lambda calculus is that the equivalence of ii expressions inside the lambda calculus is in a select few suits undecidable. This is besides avowedly of any expression in any models that has power same to the lambda calculus.