What is INF in Isabelle

I found this definition in Isabelle definition (in topological_space) nhds :: "’a ā‡’ ‘a filter" where "nhds a = (INF Sāˆˆ{S. open S āˆ§ a āˆˆ S}. principal S)" What is INF? I can’t find anything in query tab nor can I jump to definition with Ctrl+Click. >Solution : In Isabelle, INF is a constant… Read More What is INF in Isabelle