Published online by Cambridge University Press: 30 May 2022
For a subgraph
$G$
of the blow-up of a graph
$F$
, we let
$\delta ^*(G)$
be the smallest minimum degree over all of the bipartite subgraphs of
$G$
induced by pairs of parts that correspond to edges of
$F$
. Johansson proved that if
$G$
is a spanning subgraph of the blow-up of
$C_3$
with parts of size
$n$
and
$\delta ^*(G) \ge \frac{2}{3}n + \sqrt{n}$
, then
$G$
contains
$n$
vertex disjoint triangles, and presented the following conjecture of Häggkvist. If
$G$
is a spanning subgraph of the blow-up of
$C_k$
with parts of size
$n$
and
$\delta ^*(G) \ge \left(1 + \frac 1k\right)\frac n2 + 1$
, then
$G$
contains
$n$
vertex disjoint copies of
$C_k$
such that each
$C_k$
intersects each of the
$k$
parts exactly once. A similar conjecture was also made by Fischer and the case
$k=3$
was proved for large
$n$
by Magyar and Martin.
In this paper, we prove the conjecture of Häggkvist asymptotically. We also pose a conjecture which generalises this result by allowing the minimum degree conditions in each bipartite subgraph induced by pairs of parts of
$G$
to vary. We support this new conjecture by proving the triangle case. This result generalises Johannson’s result asymptotically.
Research supported in part by NSF Grant DMS 1800761.