menu_book Course Curriculum (Prolog) expand_more
negation as failure
Learn negation as failure in Prolog through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.
negation as failure is an atomic Prolog topic inside Recursion & Search. This lesson focuses on how the negation as failure construct is written, what it changes, and when it is the right tool.
Trace the example line by line. Identify the exact syntax for negation as failure, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.
Topic-specific example
available(X) :- item(X), \+ sold(X).For negation as failure, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.