Rectilinear figures are those (figures) contained by straight lines: trilateral figures being those contained by three straight lines, quadrilateral by four, and multilateral by more than four.
A nsided figure (or a rectilinear figure) is a figure given by a finite number \(n\ge 3\) of segments \(\overline{A_1B_1},\overline{A_2B_2},\ldots,\overline{A_nB_n}\), also called its sides, in such a way that
We denote nsided figures beginning with an arbitrary point and listing all points counterclockwise.
An 11sided figure \( B A K J I H G F E D C \):

Chapters: 1
Corollaries: 2 3 4 5
Definitions: 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Proofs: 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55
Propositions: 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70