The definition in you question coincide with the definition of Kuratowski for sets. See K.Kuratowski. Topology v.1 &1.V. He not use any metric.The definitions with metric Painleve, C.R. Paris v.148 (1909) and Zoretti J.Math. v.1 (1905) see K.Kuratowski. Topology v.1 &29. I.
The definition in you question coincide with the definition of Kuratowski for sets. See K.Kuratowski. Topology v.1 &1.V. He not use any metric.The definitions with metric Painleve, C.R. Paris v.148 (1909) and Zoretti J.Math. v.1 (1905) see K.Kuratowski. Topology v.1 &29. I.
I think there is not a unique answer to your question. However :
- Fréchet in his thesis in 1906 introduced the bases for topology over general sets and went on with several works on abstract sets in the following years
- the liminf definition may be due to Borel in his 1909 paper introducing the strong law of large numbers by means of (today's name of course) Borel-Cantelli lemma expressing that only a finite number of events in a sequence take place.