Involving direct communication or competition between two people.
bijective or injective
Involving one attacker and one defender.
A contest involving only one player on each side, especially of an activity often involving teams.
Involving direct communication between two people.
Matching each member of one set with exactly one member of another set.
Injective, being an injection: having the property that no two elements of the domain are mapped to the same image.
A personal relationship between two people.