===== Countable union =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $A\in \mathrm{Sequence}(X) $ |
| @#55CCEE: context     | @#55CCEE: $n\in \mathbb N\cup\{\infty\}$ |

| @#FFBB00: definiendum | @#FFBB00: $\bigcup_{j=1}^n A_j \equiv \bigcup A(\mathrm{range}(n))$ |

==== Discussion ====
==== Parents ====
=== Refinement of ===
[[Indexed union]]
=== Context ===
[[Sequence]]