4.39 Debugging and Tracing Programs
AllApplicationManualNameSummaryHelp

Availability::- use_module(library(edinburgh)).(can be autoloaded)
Sourceunknown(-Old, +New)
Edinburgh-Prolog compatibility predicate, interfacing to the ISO Prolog flag unknown. Values are trace (meaning error) and fail. If the unknown flag is set to warning, unknown/2 reports the value as trace.