; for example, we have a closed polygon of 7 vertices indicated by a letter
(setq vertex
-list '
("A" "B" "C" "D" "E" "F" "G") )
(setq all
-sides
-list '
( ("A" "B") ("B" "C") ("C" "D") ("D" "E") ("E" "F") ("F" "G") ("G" "A") ) )
(setq all
-diagonals
-list '
( ("A" "C") ("A" "D") ("A" "E") ("A" "F") ; ("A" "G") ("B" "D") ("B" "E") ("B" "F") ("B" "G")
("C" "E") ("C" "F") ("C" "G")
("D" "F") ("D" "G")
("E" "G")
)
)
'( ("A" "B" "C") ("A" "B" "D") ("A" "C" "D") ("A" "B" "E") ("A" "C" "E")
("B" "C" "E") ("A" "D" "E") ("B" "D" "E") ("C" "D" "E") ("A" "B" "F")
("A" "C" "F") ("B" "C" "F") ("A" "D" "F") ("B" "D" "F") ("C" "D" "F")
("A" "E" "F") ("B" "E" "F") ("C" "E" "F") ("D" "E" "F") ("A" "B" "G")
("A" "C" "G") ("B" "C" "G") ("A" "D" "G") ("B" "D" "G") ("C" "D" "G")
("A" "E" "G") ("B" "E" "G") ("C" "E" "G") ("D" "E" "G") ("A" "F" "G")
("B" "F" "G") ("C" "F" "G") ("D" "F" "G") ("E" "F" "G")
)
)
; to begin with, we need to calculate all these triangles