===== Subsingleton =====
==== Collection ====
| @#FFBB00: definiendum | @#FFBB00: $u$ in it |
| @#FFFDDD: for all     | @#FFFDDD: $x,y\in u$ | 
| @#55EE55: postulate   | @#55EE55: $x=y$ |

==== Discussion ====
In classical (non-constructive) set theory, a subsingleton is the empty set or a singleton.

=== Reference ===
==== Parents ====
=== Requirements ===
[[Set universe]]