SWI-Prolog -- is_process/1

Documentation
- Reference manual
- Packages
  - SWI-Prolog C-library
    - library(process): Create processes and redirect I/O

Availability::- use_module(library(process)).(can be autoloaded)

Source

[semidet]is_process(+PID)

True if PID might be a process. Succeeds for any positive integer.