*Definition [#v8e77d77]
-A non-empty closed subset C of a topological space (X,τ) is said irreducible if it is not [[reducible]].

*Reference [#m050c7c6]
-M.L. Colasante and D. Van der Zypen, ''Minimal R_1, minimal regular and minimal presober topologies'', Revista Notas de Matemática, Vol.5(1),No. 275, 2009, pp.73-84