可选的，自愿的，任意的

1. optional, voluntary, arbitrary, random, discretionary, facultative, spontaneous, any

noun (common) (futsuumeishi) nouns which may take the genitive case particle 'no' adjectival nouns or quasi-adjectives (keiyodoshi)

2. arbitrary

noun (common) (futsuumeishi) nouns which may take the genitive case particle 'no' adjectival nouns or quasi-adjectives (keiyodoshi) mathematics