cons

The resulting pair has a left half, referred to as the car (the first element, or contents of the address part of register), and a right half, referred to as the cdr (the second element, or contents of the decrement part of register).

To see this, simply rearrange the diagram: to the following equivalent: Cons can refer to the general process of memory allocation, as opposed to using destructive operations of the kind that would be used in an imperative programming language.

Church encoding is a usual way of defining data structures in pure lambda calculus, an abstract, theoretical model of computation that is closely related to Scheme.

This implementation, while academically interesting, is impractical because it renders cons cells indistinguishable from any other Scheme procedure, as well as introduces unnecessary computational inefficiencies.

[1] This encoding also has the advantage of being implementable in a statically typed language that doesn't have variants, such as Java, using interfaces instead of lambdas.