Haiku the colloquialism of the language and is closest to natural conversational rhythm, necessary to carry the weight of the hokku A haiku traditionally contains a "kigo", a word or phrase that symbolizes or implies the season of the poem and which is drawn from a "saijiki", an extensive but prescriptive list of such words. Kigo are often in the form of metonyms and can be difficult for those who lack Japanese cultural references to spot. The Bashō examples below include "kawazu", "frog" implying spring, and "shigure", a rain shower in late autumn or early winter. Kigo are not always included
Invariant of a binary form for the ring of covariants. showed that the ring of invariants of a degree 8 form is generated by 9 invariants of degrees 2, 3, 4, 5, 6, 7, 8, 9, 10, and the ring of covariants is generated by 69 covariants. August von Gall () and confirmed the generators for the ring of invariants and showed that the ideal of relations between them is generated by elements of degrees 16, 17, 18, 19, 20. showed that the algebra of invariants of a degree 9 form is generated by 92 invariants. Cröni, Hagedorn, and Brouwer computed 476 covariants, and Lercier