**2. Preliminaries**

In this section, we introduce the basic knowledge and concepts, which are essential for this work.

**Definition 1.** *Let* D *be the space consisting of all real-valued functions ϕ*(*t*) *with continuous derivatives of all orders and compact support. The support of ϕ*(*t*) *is the closure of the set of all elements t* ∈ R *such that ϕ*(*t*) = 0*. Then ϕ*(*t*) *is called a test function.*

**Definition 2.** *A distribution T is a continuous linear functional on the space* D*. The space of all such distributions is denoted by* D-*.*

For every *T* ∈ D- and *ϕ*(*t*) ∈ D, the value that *T* acts on *ϕ*(*t*) is denoted by *<sup>T</sup>*, *ϕ*(*t*). Note that *<sup>T</sup>*, *ϕ*(*t*) ∈ R.
