Trellis 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 6 stitches, plus 5.
Row 1 (RS): P4, *Slip 3 wyif, P3; rep from * to last st, P1.
Row 2 (WS): K4, *Slip 3 wyib, K3; rep from * to last st, K1.
Row 3: P4, *K3, P3; rep from * to last st, P1.
Row 4: Knit.
Row 5: Purl.
Row 6: Knit.
Row 7: P5, *K1 uls, P5; rep from * to end.
Row 8: Knit.
Row 9: P1, *Slip 3 wyif, P3; rep from * to last 4 sts, Slip 3 wyif, P1.
Row 10: K1, *Slip 3 wyib, K3; rep from * to last 4 sts, Slip 3 wyib, K1.
Row 11: P1, *Slip 3 wyif, P3 ; rep from * to last 4 sts, Slip 3 wyif, P1.
Row 12: Knit.
Row 13: Purl.
Row 14: Knit.
Row 15: P2, *K1 uls, P5; rep from * to last 3 sts, K1 uls, P2.
Row 16: Knit.
Rep Rows 1-16.