Published online by Cambridge University Press: 30 May 2022
For a subgraph  $G$ of the blow-up of a graph
$G$ of the blow-up of a graph  $F$, we let
$F$, we let  $\delta ^*(G)$ be the smallest minimum degree over all of the bipartite subgraphs of
$\delta ^*(G)$ be the smallest minimum degree over all of the bipartite subgraphs of  $G$ induced by pairs of parts that correspond to edges of
$G$ induced by pairs of parts that correspond to edges of  $F$. Johansson proved that if
$F$. Johansson proved that if  $G$ is a spanning subgraph of the blow-up of
$G$ is a spanning subgraph of the blow-up of  $C_3$ with parts of size
$C_3$ with parts of size  $n$ and
$n$ and  $\delta ^*(G) \ge \frac{2}{3}n + \sqrt{n}$, then
$\delta ^*(G) \ge \frac{2}{3}n + \sqrt{n}$, then  $G$ contains
$G$ contains  $n$ vertex disjoint triangles, and presented the following conjecture of Häggkvist. If
$n$ vertex disjoint triangles, and presented the following conjecture of Häggkvist. If  $G$ is a spanning subgraph of the blow-up of
$G$ is a spanning subgraph of the blow-up of  $C_k$ with parts of size
$C_k$ with parts of size  $n$ and
$n$ and  $\delta ^*(G) \ge \left(1 + \frac 1k\right)\frac n2 + 1$, then
$\delta ^*(G) \ge \left(1 + \frac 1k\right)\frac n2 + 1$, then  $G$ contains
$G$ contains  $n$ vertex disjoint copies of
$n$ vertex disjoint copies of  $C_k$ such that each
$C_k$ such that each  $C_k$ intersects each of the
$C_k$ intersects each of the  $k$ parts exactly once. A similar conjecture was also made by Fischer and the case
$k$ parts exactly once. A similar conjecture was also made by Fischer and the case  $k=3$ was proved for large
$k=3$ was proved for large  $n$ by Magyar and Martin.
$n$ 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.
$G$ 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.
 $F$
-factors in hypergraphs via absorption. Graphs Combin 31(3) 679–712.CrossRefGoogle Scholar
$F$
-factors in hypergraphs via absorption. Graphs Combin 31(3) 679–712.CrossRefGoogle Scholar