  In this paper, we consider a structural and geometric property of graphs,
namely the presence of large expanders. The problem of finding such structures
was first considered by Krivelevich [SIAM J. Disc. Math. 32 1 (2018)]. Here, we
show that the problem of finding a large induced subgraph that is an expander
can be reduced to the simpler problem of finding a topological minor that is an
expander. Our proof is constructive, which is helpful in an algorithmic
setting. We also show that every large subgraph of an expander graph contains a
large subgraph which is itself an expander.
