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Facts & Rules
fact rule predicate atom variable anonymous variable compound term arity query unification
Lists
empty list head tail pattern member append length recursive list sum maplist select reverse nth0
Recursion & Search
base case recursive case backtracking choice point cut fail once negation as failure disjunction if then else
Arithmetic
is numeric comparison term comparison mod integer division between succ max min arithmetic recursion
Control & Meta
call findall bagof setof forall catch throw setup_call_cleanup repeat once meta current_predicate
DCGs
DCG rule terminal list nonterminal phrase DCG arguments semicontext recursive grammar optional grammar list grammar token grammar
Constraints
CLPFD domain #= #\= #< #> ins all_distinct labeling reified constraint sum constraint
Dynamic & Modules
dynamic predicate assertz asserta retract retractall abolish module declaration export list use_module multifile
Prolog / Facts & Rules

arity

Learn arity in Prolog through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Beginner

arity is an atomic Prolog topic inside Facts & Rules. This lesson focuses on how the arity construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for arity, 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

prolog-01-08-arity.pl
prolog Try It Live 
edge(a,b).
edge(a,b,5).  % edge/2 and edge/3 are different predicates
Edge case / engineering note

For arity, 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.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

arity Mastery Check →
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