A.14 library(debug): Print debug messages and test assertions
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Availability::- use_module(library(debug)).(can be autoloaded)
Source[semidet]debugging(+Topic)
[nondet]debugging(-Topic)
[nondet]debugging(?Topic, ?Bool)
Examine debug topics. The form debugging(+Topic) may be used to perform more complex debugging tasks. A typical usage skeleton is: 
      (   debugging(mytopic)
      ->  <perform debugging actions>
      ;   true
      ),
      ...

The other two calls are intended to examine existing and enabled debugging tokens and are typically not used in user programs.