<dependency>
  <groupId>io.projectreactor</groupId>
  <artifactId>reactor-core</artifactId>
  <version>3.4.21</version>
</dependency>

implementation 'io.projectreactor:reactor-core:3.4.21'

implementation("io.projectreactor:reactor-core:3.4.21")

libraryDependencies += "io.projectreactor" % "reactor-core" % "3.4.21"

@Grapes(
  @Grab(group='io.projectreactor', module='reactor-core', version='3.4.21')
)

<dependency org="io.projectreactor" name="reactor-core" rev="3.4.21" />

[io.projectreactor/reactor-core "3.4.21"]

'io.projectreactor:reactor-core:jar:3.4.21'