For more details we refer the reader to .
We refer the reader to the body of the paper for details.
For a comprehensive treatment and for references to the extensive literature on the subject one may refer to the book [M] by Markov.
The interested reader is referred to  for further information. [Note the double r in referred.]
In the physical context already referred to, $K$ is the density of ......
This theorem will hereafter be referred to as the minimum principle.
We refer to these as homogeneous Sobolev spaces.
We shall also refer to a point as backward nonsingular, with the obvious analogous meaning.
In the following, all topological notions refer to the weak topology of $Y$.
To be precise, refer to the notation in Theorem 1 and define ......