If T1 and T2 are two Turing machines. The composite can be represented using theexpression:

The expression for the composite of two Turing machines T1 and T2 can be represented as T1;T2. This means that the output of Turing machine T1 is fed as the input to Turing machine T2.

Here are the steps to understand this:

1. A Turing machine is a theoretical machine used in the field of computation and computer science. It is a mathematical model of computation that defines an abstract machine, which manipulates symbols on a strip of tape according to a table of rules.

2. The composite of two Turing machines T1 and T2, represented as T1;T2, means that the two machines are connected in a series.

3. The output from the first Turing machine (T1) is used as the input for the second Turing machine (T2).

4. This is similar to the concept of function composition in mathematics, where the output of one function becomes the input of another.

5. So, in the context of Turing machines, the composite T1;T2 represents a new Turing machine that performs the operations of T1 followed by the operations of T2.