Relative phantom maps

Kouyemon Iriye, Daisuke Kishimoto, Takahiro Matsushita

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


The de Bruijn–Erd?os theorem states that the chromatic number of an infinite graph equals the maximum of the chromatic numbers of its finite subgraphs. Such determination by finite subobjects appears in the definition of a phantom map, which is classical in algebraic topology. The topological method in combinatorics connects these two, which leads us to define the relative version of a phantom map: a map f: X → Y is called a relative phantom map to a map φ: B → Y if the restriction of f to any finite dimensional skeleton of X lifts to B through φ, up to homotopy. There are two kinds of maps which are obviously relative phantom maps: (1) the composite of a map X→B with φ; (2) a usual phantom map X→Y. A relative phantom map of type (1) is called trivial, and a relative phantom map out of a suspension which is a sum of (1) and (2) is called relatively trivial. We study the (relative) triviality of relative phantom maps from a suspension, and in particular, we give rational homotopy conditions for the (relative) triviality.

Original languageEnglish
Pages (from-to)341-362
Number of pages22
JournalAlgebraic and Geometric Topology
Issue number1
Publication statusPublished - Feb 6 2019
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geometry and Topology


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