Exchange Operation as Replacement Operations

Example of use of Replacement Operation
Let $x$ and $y$ be variables whose values are to be exchanged.

The exchange operation on $x$ and $y$ can be implemented using replacement operations.

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.

Proof
Observing the values of the variables after each replacement operation:

Hence the result.