- Documentation
- Reference manual
- The SWI-Prolog library
- library(aggregate): Aggregation operators on backtrackable predicates
- library(apply): Apply predicates on a list
- library(assoc): Association lists
- library(broadcast): Broadcast and receive event notifications
- library(charsio): I/O on Lists of Character Codes
- library(check): Consistency checking
- library(clpb): CLP(B): Constraint Logic Programming over Boolean Variables
- library(clpfd): CLP(FD): Constraint Logic Programming over Finite Domains
- library(clpqr): Constraint Logic Programming over Rationals and Reals
- library(csv): Process CSV (Comma-Separated Values) data
- library(debug): Print debug messages and test assertions
- library(error): Error generating support
- library(gensym): Generate unique identifiers
- library(iostream): Utilities to deal with streams
- library(lists): List Manipulation
- library(main): Provide entry point for scripts
- library(nb_set): Non-backtrackable set
- library(www_browser): Activating your Web-browser
- library(option): Option list processing
- library(optparse): command line parsing
- library(ordsets): Ordered set manipulation
- library(pairs): Operations on key-value lists
- library(persistency): Provide persistent dynamic predicates
- library(pio): Pure I/O
- library(predicate_options): Declare option-processing of predicates
- library(prolog_pack): A package manager for Prolog
- library(prolog_xref): Cross-reference data collection library
- library(quasi_quotations): Define Quasi Quotation syntax
- library(random): Random numbers
- library(readutil): Reading lines, streams and files
- library(record): Access named fields in a term
- library(registry): Manipulating the Windows registry
- library(simplex): Solve linear programming problems
- library(solution_sequences): Modify solution sequences
- library(tabling): Tabled execution (SLG)
- library(thread_pool): Resource bounded thread management
- library(ugraphs): Unweighted Graphs
- library(url): Analysing and constructing URL
- library(varnumbers): Utilities for numbered terms
- library(yall): Lambda expressions

- The SWI-Prolog library
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- Reference manual

## A.39 library(varnumbers): Utilities for numbered terms

- See also
- numbervars/4, =@=/2 (variant/2).
- Compatibility
- This library was introduced by Quintus and available in many related implementations, although not with exactly the same set of predicates.

This library provides the inverse functionality of the built-in
numbervars/3.
Note that this library suffers from the known issues that '$VAR'(X) is a
normal Prolog term and, -unlike the built-in numbervars-, the inverse
predicates do *not* process cyclic terms. The following predicate
is true for any acyclic term that contains no '$VAR'(X),
`integer(X)`

terms and no constraint variables:

always_true(X) :- copy_term(X, X2), numbervars(X), varnumbers(X, Copy), Copy =@= X2.

- [det]
**numbervars**(`+Term`) - Number variables in
`Term`using $VAR(N). Equivalent to`numbervars(Term, 0, _)`

.- See also
- numbervars/3, numbervars/4

- [det]
**varnumbers**(`+Term, -Copy`) - Inverse of numbervars/1.
Equivalent to
`varnumbers(Term, 0, Copy)`

. - [det]
**varnumbers**(`+Term, +Start, -Copy`) - Inverse of numbervars/3.
True when
`Copy`is a copy of`Term`with all variables numbered`>=`

`Start`consistently replaced by fresh variables. Variables in`Term`are*shared*with`Copy`rather than replaced by fresh variables.- Errors
`domain_error(acyclic_term, Term)`

if`Term`is cyclic.- Compatibility
- Quintus, SICStus. Not in YAP version of this library

- [det]
**max_var_number**(`+Term, +Start, -Max`) - True when
`Max`is the max of`Start`and the highest numbered $VAR(N) term.- author
- Vitor Santos Costa
- Compatibility
- YAP

- [det]
**varnumbers_names**(`+Term, -Copy, -VariableNames`) - If
`Term`is a term with numbered and named variables using the reserved term '$VAR'(X),`Copy`is a copy of`Term`where each '$VAR'(X) is consistently replaced by a fresh variable and Bindings is a list`X = Var`

, relating the`X`terms with the variable it is mapped to.- See also
- numbervars/3, varnumbers/3, read_term/3
using the
`variable_names`

option.