### Restriction #1: A polygon's first 3 vertices must form a triangle

The triangle can be extremely shallow. This is legal:

```
POLYSTART
MAKE "savepos POSXYZ
FORWARD 100
RIGHT 0.00000001 ; very small angles are okay
FORWARD 100
SETPOS :saveposxyz
POLYEND
```

This is NOT legal (even though it produces a convex polygon):

```
POLYSTART
MAKE "savepos POSXYZ
FORWARD 50
FORWARD 50 ; error can't have straight angles
RIGHT 90
FORWARD 100
SETPOS :saveposxyz
POLYEND
```