<http://ns.inria.fr/covid19/PMC7274701#body_text>	<http://purl.org/dc/terms/subject>	"Closure operators" .
<http://ns.inria.fr/covid19/PMC7274701#body_text>	<http://purl.org/dc/terms/subject>	"Logical expressions" .
<http://ns.inria.fr/covid19/PMC7274701#body_text>	<http://purl.org/dc/terms/subject>	"Morphisms" .
<http://ns.inria.fr/covid19/PMC7274701#body_text>	<http://purl.org/dc/terms/subject>	"Mathematical proofs" .