pull the yarn tight to prevent holes and loose stitches next to the buttonhole.
8. now cast-on stitches, for example by knitting them on, or by using the backward-loop method. cast-on the number of stitches you have cast-off earlier, plus 1 extra. in the example i cast-on a total of 4 stitches.
9. turn piece again and slip the first stitch purl-wise from your left to your right needle.
10. pass the second stitch on your right needle (the last cast-on extra stitch) over the first stitch.
11. now slip the first stitch from your right needle back to the left needle and continue knitting according to your pattern. 