Exchange Operation as Replacement Operations

Theorem
The exchange operation can be implemented using replacement operations.

Proof
Let $x$ and $y$ be the variables whose values are to be exchanged.

Let $t$ be a third variable which has been established for this purpose.

Then the sequence of replacement operations:
 * $t \gets x$
 * $x \gets y$
 * $y \gets t$

performs the task.