1. Cf. Enriques, quoted in note to § 8·1.
2. Such a curve can be projected into a plane quintic. It has a double infinity of pentasecant planes (cut by [4]'s through the given one) and the complete intersection of the Q 4's containing it is a Veronese surface (see third footnote to § 8·1).
3. These, and other intersection properties given in the sequel, are found from the plane representation.
4. Both of these sets give the family (2; 1, 0, 0, 0), which is also given by the sets (l 14, l 23, l 15, l 34, l 12), (l 12, l 34, l 15, l 24, l 13, ) of the former type and (l 25, l 12, l 13, l 14, l 34), (l 35, l 12, l 24, l 14, l 13) of the latter type. The change from one of these sets to another of the same type is made by interchanging 2 and 3, or 3 and 4, or 4 and 2 in the suffixes.