元となった辞書の項目
ordinal number
noun
意味（3）
(set
theory)
Such
a
number
generalised
to
correspond
to
any
cardinal
number
(the
size
of
some
set);
formally,
the
order
type
of
some
well-ordered
set
of
some
cardinality
a,
which
represents
an
equivalence
class
of
well-ordered
sets
(exactly
those
of
cardinality
a)
under
the
equivalence
relation
"existence
of
an
order-preserving
bijection".
