noun
bijection
Technical term in mathematics for a function that is both injective (one-to-one) and surjective (onto).
全単射が存在するとき、二つの集合は同じ濃度を持つ。
When a bijection exists, the two sets have the same cardinality.
全射 (surjection) is an onto function, but not necessarily one-to-one. 全単射 combines both properties.
Compound of 全 (all, entire), 単 (single, simple), and 射 (mapping, projection). The term is a direct translation of the mathematical concept 'bijection'.