Butterfly Slip Stitch Pattern

How to knit the K1 uls.
Take the right-hand needle under the slipped threads, then pick up the next st on the left-hand needle and knit this st and the slipped threads together.

Pattern
Cast on a multiple of 10 sts, plus 9.
Rows 1, 3, 5, 7 (RS): K2, *Slip 5 wyif, K5; rep from * to last 7 sts, Slip 5 wyif, K2.
Row 2 and all WS rows: Purl.
Row 9: K4, *K1 uls, K9; rep from * to last 5 sts, K1 uls, K4.
Rows 11, 13, 15, 17: K7, *Slip 5 wyif, K5; rep from * to last 2 sts, K2.
Row 19: K9, *K1 uls, K9; rep from * to end.
Row 20: Purl.
Rep Rows 1-20.