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Section 2.3 P(rojective) SET

Each P card consists of two SET cards “glued together”.
Figure 2.3.1. A PSET card

Definition 2.3.2.

A PSET is a collection of 3 cards such that the cards may be flipped over in such a way so that both the top and the bottom form SETs.

Activity 2.3.2.

(a)

What PSETs can you find here?
Figure 2.3.3. 12 SET cards.

Activity 2.3.4.

(a)

What card(s) can you add to form a PSET?

(b)

Out of these cards, how many PSETs can you find?

(c)

Pick any two cards, can you find what card(s) if any will complete a set? How many PSETs can you find? Repeat.

Remark 2.3.4.

We will let a Pline in the PSET context to be a collection of 4 cards so that every 3 card subset forms a PSET.

Activity 2.3.5.

(a)

Pick any three cards who do not form a PSET and arrange them in a corner of the 3×3 grid:

(b)

Fill out this grid so that each line forms a Pline.

(c)

For each pair of cards on this grid, do they lie on exactly one Pline?