https://en.wikipedia.org/wiki/Ideal Ideal (抜粋) Mathematics Ideal (ring theory), special subsets of a ring considered in abstract algebra Ideal, special subsets of a semigroup Ideal (order theory), special kind of lower sets of an order Ideal (set theory), a collection of sets regarded as "small" or "negligible" Ideal (Lie algebra), a particular subset in a Lie algebra Ideal point, a boundary point in hyperbolic geometry Ideal triangle, a triangle in hyperbolic geometry whose vertices are ideal points (引用終り)
