We leave the details to the reader.
We leave it to the reader to verify that ...... [Note that the it is necessary here.]
For more details we refer the reader to .
If nothing else, I hope to convince my readers that Segal's theorem deserves recognition as a profound contribution to Gaussian analysis.
It may be worth reminding the reader that ......
The reader is cautioned that our notation is in conflict with that of .
The reader is assumed to be familiar with elementary $K$-theory.
The interested reader is referred to  for further information. [Note the double r in referred.]
At this point, the reader is urged to review the definitions of ......
The reader might want to compare this remark with [2, Cor. 3].
For the convenience of the reader, we repeat the main points. [Or: For the reader's convenience]