From type/Proc/Async

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multi method kill(Proc::Async:D: Signal:D \signal = SIGHUP)

multi method kill(Proc::Async:D: Int:D \signal)

multi method kill(Proc::Async:D: Str:D \signal)

Sends a signal to the running program. The signal can be a signal name ("KILL" or "SIGKILL"), an integer (9) or an element of the Signal enum (Signal::SIGKILL); by default and with no argument, the SIGHUP signal will be used.