Glencore took a $US7.7 billion write-down in 2013 on the $US29 billion "merger" with Xstrata it executed the same year, with the bulk of that taken on goodwill.
Take context from the input text and decide on the accurate relationship between 'Xstrata' and 'Glencore' from the options provided.
Options: platform, distributed by, owned by, operator