Physics Friday: Crocheted Mathematical Objects

I made a Klein bottle.

I used double crochet and worked mostly in rounds. I used double crochet so it would work up quickly and so the rows that are worked back and forth wouldn't stand out so much against the ones worked in rounds. I sort of made it up as I went. Here's my pattern:

Work in linked rounds, which means to slip stitch the last stitch into the third chain of the first stitch in the round. Start each round with a chain of 3 and count it as one double crochet. This happens every round so I won't mention it every time. Work in double crochet.
Chain 12 and join with a slip stitch to make a round
Rnd 1: double crochet each stitch around (12)
Rnd 2: work each stitch
Rnd 3: increase in every other stitch, double crochet twice in a stitch to increase (18)
Rnd 4: increase in every other (27)
Rnd 5: inc every other (40)

Rnd 6: work each stitch
Rnd 7: decrease every third. work every 3rd and 4th stitch together (30)
Row 8: turn work. decrease every 3rd (22)
Row 9: turn work. decrease every 3rd (16)

Rnd 10: work as a round slipping into first stitch across gap. decrease every 3rd (12)
Rnd 11-17: work in every stitch.

finishing: slip stitch to join. cut leaving a long tail for sewing. Invert start end and push it through the gap made by the rows. Sew to other end.