Singleton (Mathematics): Mathematics, Set (Mathematics), Unique, If and Only If, Cardinality

Intersection (set theory): theory), Mathematics, Set (mathematics), If and only

Subspace Topology: Topology, Mathematics, Topological Space, Subset, If and Only if, Intersection (Set Theory)

Without Loss of Generality: Mathematics, If and Only If, Symmetry, Theorem, Up To

Trivial Semigroup: Mathematics, Semigroup, Cardinality