Of course the same query with just a changed graph name and less whitespace works at https://sparql.rhea-db.org as well. Because both #ontobee and #rhea decided not to remodel #ChEBI (no matter how much we might have wanted to). This is real #interoperability

https://sparql.rhea-db.org/sparql/?query=PREFIX+CHEBI%3A+%3Chttp%3A%2F%2Fpurl.obolibrary.org%2Fobo%2FCHEBI_%3E%0D%0ASELECT+%3Fchebi+%3Flabel+%3Fcomment%0D%0A%7B+GRAPH+%3Chttp%3A%2F%2Fsparql.rhea-db.org%2Fchebi%3E+%7B+%3Fchebi+%3Chttp%3A%2F%2Fpurl.obolibrary.org%2Fobo%2FIAO_0000115%3E+%3Fcomment+.%0D%0AFILTER%28CONTAINS%28%3Fcomment%2C+%22mixture%22%29%29%0D%0AOPTIONAL+%7B%0D%0A%3Fchebi+rdfs%3AsubClassOf+CHEBI%3A60004+.+%0D%0ABIND%28true+AS+%3FisMixture%29%0D%0A%7D%0D%0AFILTER%28%21BOUND%28%3FisMixture%29%29%0D%0AFILTER%28%3Fchebi+%21%3D+CHEBI%3A60004%29%0D%0A%3Fchebi+rdfs%3Alabel+%3Flabel+.%0D%0A%7D%7D&format=html&query=PREFIX+CHEBI%3A+%3Chttp%3A%2F%2Fpurl.obolibrary.org%2Fobo%2FCHEBI_%3E%0D%0ASELECT+%3Fchebi+%3Flabel+%3Fcomment%0D%0A%7B+GRAPH+%3Chttp%3A%2F%2Fsparql.rhea-db.org%2Fchebi%3E+%7B+%3Fchebi+%3Chttp%3A%2F%2Fpurl.obolibrary.org%2Fobo%2FIAO_0000115%3E+%3Fcomment+.%0D%0AFILTER%28CONTAINS%28%3Fcomment%2C+%22mixture%22%29%29%0D%0AOPTIONAL+%7B%0D%0A%3Fchebi+rdfs%3AsubClassOf+CHEBI%3A60004+.+%0D%0ABIND%28true+AS+%3FisMixture%29%0D%0A%7D%0D%0AFILTER%28%21BOUND%28%3FisMixture%29%29%0D%0AFILTER%28%3Fchebi+%21%3D+CHEBI%3A60004%29%0D%0A%3Fchebi+rdfs%3Alabel+%3Flabel+.%0D%0A%7D%7D