Finite subgraphs of uncountably chromatic graphs
Abstract
It is consistent that for every monotonically increasing function f:omega->omega there is a graph with size and chromatic number aleph1 in which every n-chromatic subgraph has at least f(n) elements (n >= 3). This solves a $250 problem of Erdos. It is also consistent that there is a graph X with Chr(X)=|X|= aleph1 such that if Y is a graph all whose finite subgraphs occur in X then Chr(Y)<=aleph2 (so the Taylor conjecture may fail).
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