Add staged inter-distance propagation with variable separation

Makefile.dep

@@ -35243,3 +35243,139 @@ test/int/min-distance$(OBJSUFFIX) test/int/min-distance$(SBJSUFFIX): \
 	./gecode/support/static-stack.hpp ./gecode/support/thread.hpp ./gecode/support/thread/thread.hpp \
 	./gecode/support/timer.hpp ./test/int.hh ./test/int.hpp \
 	./test/test.hh ./test/test.hpp
+gecode/int/inter-distance$(OBJSUFFIX) gecode/int/inter-distance$(SBJSUFFIX): \
+	./gecode/int.hh ./gecode/int/array-traits.hpp ./gecode/int/array.hpp \
+	./gecode/int/branch.hpp ./gecode/int/branch/action.hpp ./gecode/int/branch/afc.hpp \
+	./gecode/int/branch/assign.hpp ./gecode/int/branch/chb.hpp ./gecode/int/branch/traits.hpp \
+	./gecode/int/branch/val.hpp ./gecode/int/branch/var.hpp ./gecode/int/channel.hpp \
+	./gecode/int/distinct.hh ./gecode/int/distinct/bnd.hpp ./gecode/int/distinct/cbs.hpp \
+	./gecode/int/distinct/dom-ctrl.hpp ./gecode/int/distinct/dom.hpp ./gecode/int/distinct/eqite.hpp \
+	./gecode/int/distinct/graph.hpp ./gecode/int/distinct/ter-dom.hpp ./gecode/int/distinct/val.hpp \
+	./gecode/int/div.hh ./gecode/int/div.hpp ./gecode/int/exception.hpp \
+	./gecode/int/extensional.hpp ./gecode/int/extensional/dfa.hpp ./gecode/int/extensional/tuple-set.hpp \
+	./gecode/int/int-set-1.hpp ./gecode/int/int-set-2.hpp ./gecode/int/inter-distance.hh \
+	./gecode/int/ipl.hpp ./gecode/int/irt.hpp ./gecode/int/limits.hpp \
+	./gecode/int/propagator.hpp ./gecode/int/reify.hpp ./gecode/int/rel.hh \
+	./gecode/int/rel/eq.hpp ./gecode/int/rel/lex.hpp ./gecode/int/rel/lq-le.hpp \
+	./gecode/int/rel/nq.hpp ./gecode/int/trace.hpp ./gecode/int/trace/bool-delta.hpp \
+	./gecode/int/trace/bool-trace-view.hpp ./gecode/int/trace/int-delta.hpp ./gecode/int/trace/int-trace-view.hpp \
+	./gecode/int/trace/traits.hpp ./gecode/int/var-imp.hpp ./gecode/int/var-imp/bool.hpp \
+	./gecode/int/var-imp/delta.hpp ./gecode/int/var-imp/int.hpp ./gecode/int/var/bool.hpp \
+	./gecode/int/var/int.hpp ./gecode/int/var/print.hpp ./gecode/int/view-val-graph.hh \
+	./gecode/int/view-val-graph/bi-link.hpp ./gecode/int/view-val-graph/comb-ptr-flag.hpp ./gecode/int/view-val-graph/edge.hpp \
+	./gecode/int/view-val-graph/graph.hpp ./gecode/int/view-val-graph/iter-prune-val.hpp ./gecode/int/view-val-graph/node.hpp \
+	./gecode/int/view.hpp ./gecode/int/view/bool-test.hpp ./gecode/int/view/bool.hpp \
+	./gecode/int/view/cached.hpp ./gecode/int/view/constint.hpp ./gecode/int/view/int.hpp \
+	./gecode/int/view/iter.hpp ./gecode/int/view/minus.hpp ./gecode/int/view/neg-bool.hpp \
+	./gecode/int/view/offset.hpp ./gecode/int/view/print.hpp ./gecode/int/view/rel-test.hpp \
+	./gecode/int/view/scale.hpp ./gecode/int/view/zero.hpp ./gecode/iter.hh \
+	./gecode/iter/ranges-add.hpp ./gecode/iter/ranges-append.hpp ./gecode/iter/ranges-array.hpp \
+	./gecode/iter/ranges-cache.hpp ./gecode/iter/ranges-compl.hpp ./gecode/iter/ranges-diff.hpp \
+	./gecode/iter/ranges-empty.hpp ./gecode/iter/ranges-inter.hpp ./gecode/iter/ranges-list.hpp \
+	./gecode/iter/ranges-map.hpp ./gecode/iter/ranges-minmax.hpp ./gecode/iter/ranges-minus.hpp \
+	./gecode/iter/ranges-negative.hpp ./gecode/iter/ranges-offset.hpp ./gecode/iter/ranges-operations.hpp \
+	./gecode/iter/ranges-positive.hpp ./gecode/iter/ranges-rangelist.hpp ./gecode/iter/ranges-scale.hpp \
+	./gecode/iter/ranges-singleton-append.hpp ./gecode/iter/ranges-singleton.hpp ./gecode/iter/ranges-size.hpp \
+	./gecode/iter/ranges-union.hpp ./gecode/iter/ranges-values.hpp ./gecode/iter/values-array.hpp \
+	./gecode/iter/values-bitset.hpp ./gecode/iter/values-bitsetoffset.hpp ./gecode/iter/values-inter.hpp \
+	./gecode/iter/values-list.hpp ./gecode/iter/values-map.hpp ./gecode/iter/values-minus.hpp \
+	./gecode/iter/values-negative.hpp ./gecode/iter/values-offset.hpp ./gecode/iter/values-positive.hpp \
+	./gecode/iter/values-ranges.hpp ./gecode/iter/values-singleton.hpp ./gecode/iter/values-union.hpp \
+	./gecode/iter/values-unique.hpp ./gecode/kernel.hh ./gecode/kernel/archive.hpp \
+	./gecode/kernel/branch/action.hpp ./gecode/kernel/branch/afc.hpp ./gecode/kernel/branch/chb.hpp \
+	./gecode/kernel/branch/filter.hpp ./gecode/kernel/branch/merit.hpp ./gecode/kernel/branch/print.hpp \
+	./gecode/kernel/branch/tiebreak.hpp ./gecode/kernel/branch/traits.hpp ./gecode/kernel/branch/val-commit.hpp \
+	./gecode/kernel/branch/val-sel-commit.hpp ./gecode/kernel/branch/val-sel.hpp ./gecode/kernel/branch/val.hpp \
+	./gecode/kernel/branch/var.hpp ./gecode/kernel/branch/view-sel.hpp ./gecode/kernel/branch/view-val.hpp \
+	./gecode/kernel/branch/view.hpp ./gecode/kernel/core.hpp ./gecode/kernel/data/array.hpp \
+	./gecode/kernel/data/rnd.hpp ./gecode/kernel/data/shared-array.hpp ./gecode/kernel/data/shared-data.hpp \
+	./gecode/kernel/exception.hpp ./gecode/kernel/gpi.hpp ./gecode/kernel/macros.hpp \
+	./gecode/kernel/memory/allocators.hpp ./gecode/kernel/memory/config.hpp ./gecode/kernel/memory/manager.hpp \
+	./gecode/kernel/memory/region.hpp ./gecode/kernel/modevent.hpp ./gecode/kernel/propagator/advisor.hpp \
+	./gecode/kernel/propagator/pattern.hpp ./gecode/kernel/propagator/subscribed.hpp ./gecode/kernel/propagator/wait.hpp \
+	./gecode/kernel/range-list.hpp ./gecode/kernel/shared-object.hpp ./gecode/kernel/shared-space-data.hpp \
+	./gecode/kernel/trace/filter.hpp ./gecode/kernel/trace/general.hpp ./gecode/kernel/trace/print.hpp \
+	./gecode/kernel/trace/recorder.hpp ./gecode/kernel/trace/tracer.hpp ./gecode/kernel/trace/traits.hpp \
+	./gecode/kernel/var-imp.hpp ./gecode/kernel/var-type.hpp ./gecode/kernel/var.hpp \
+	./gecode/kernel/view.hpp ./gecode/search.hh ./gecode/search/bab.hpp \
+	./gecode/search/base.hpp ./gecode/search/build.hpp ./gecode/search/cutoff.hpp \
+	./gecode/search/dfs.hpp ./gecode/search/engine.hpp ./gecode/search/exception.hpp \
+	./gecode/search/lds.hpp ./gecode/search/options.hpp ./gecode/search/pbs.hpp \
+	./gecode/search/rbs.hpp ./gecode/search/sebs.hpp ./gecode/search/seq/dead.hh \
+	./gecode/search/statistics.hpp ./gecode/search/stop.hpp ./gecode/search/support.hh \
+	./gecode/search/trace-recorder.hpp ./gecode/search/tracer.hpp ./gecode/search/traits.hpp \
+	./gecode/support.hh ./gecode/support/allocator.hpp ./gecode/support/auto-link.hpp \
+	./gecode/support/bitset-base.hpp ./gecode/support/bitset-offset.hpp ./gecode/support/bitset.hpp \
+	./gecode/support/block-allocator.hpp ./gecode/support/cast.hpp gecode/support/config.hpp \
+	./gecode/support/dynamic-array.hpp ./gecode/support/dynamic-queue.hpp ./gecode/support/dynamic-stack.hpp \
+	./gecode/support/exception.hpp ./gecode/support/failpoint.hpp ./gecode/support/hash.hpp \
+	./gecode/support/heap.hpp ./gecode/support/hw-rnd.hpp ./gecode/support/int-type.hpp \
+	./gecode/support/macros.hpp ./gecode/support/marked-pointer.hpp ./gecode/support/random.hpp \
+	./gecode/support/ref-count.hpp ./gecode/support/run-jobs.hpp ./gecode/support/sort.hpp \
+	./gecode/support/static-stack.hpp ./gecode/support/thread.hpp ./gecode/support/thread/thread.hpp \
+	./gecode/support/timer.hpp
+test/int/inter-distance$(OBJSUFFIX) test/int/inter-distance$(SBJSUFFIX): \
+	./gecode/int.hh ./gecode/int/array-traits.hpp ./gecode/int/array.hpp \
+	./gecode/int/branch.hpp ./gecode/int/branch/action.hpp ./gecode/int/branch/afc.hpp \
+	./gecode/int/branch/assign.hpp ./gecode/int/branch/chb.hpp ./gecode/int/branch/traits.hpp \
+	./gecode/int/branch/val.hpp ./gecode/int/branch/var.hpp ./gecode/int/channel.hpp \
+	./gecode/int/div.hh ./gecode/int/div.hpp ./gecode/int/exception.hpp \
+	./gecode/int/extensional.hpp ./gecode/int/extensional/dfa.hpp ./gecode/int/extensional/tuple-set.hpp \
+	./gecode/int/int-set-1.hpp ./gecode/int/int-set-2.hpp ./gecode/int/ipl.hpp \
+	./gecode/int/irt.hpp ./gecode/int/limits.hpp ./gecode/int/propagator.hpp \
+	./gecode/int/reify.hpp ./gecode/int/trace.hpp ./gecode/int/trace/bool-delta.hpp \
+	./gecode/int/trace/bool-trace-view.hpp ./gecode/int/trace/int-delta.hpp ./gecode/int/trace/int-trace-view.hpp \
+	./gecode/int/trace/traits.hpp ./gecode/int/var-imp.hpp ./gecode/int/var-imp/bool.hpp \
+	./gecode/int/var-imp/delta.hpp ./gecode/int/var-imp/int.hpp ./gecode/int/var/bool.hpp \
+	./gecode/int/var/int.hpp ./gecode/int/var/print.hpp ./gecode/int/view.hpp \
+	./gecode/int/view/bool-test.hpp ./gecode/int/view/bool.hpp ./gecode/int/view/cached.hpp \
+	./gecode/int/view/constint.hpp ./gecode/int/view/int.hpp ./gecode/int/view/iter.hpp \
+	./gecode/int/view/minus.hpp ./gecode/int/view/neg-bool.hpp ./gecode/int/view/offset.hpp \
+	./gecode/int/view/print.hpp ./gecode/int/view/rel-test.hpp ./gecode/int/view/scale.hpp \
+	./gecode/int/view/zero.hpp ./gecode/iter.hh ./gecode/iter/ranges-add.hpp \
+	./gecode/iter/ranges-append.hpp ./gecode/iter/ranges-array.hpp ./gecode/iter/ranges-cache.hpp \
+	./gecode/iter/ranges-compl.hpp ./gecode/iter/ranges-diff.hpp ./gecode/iter/ranges-empty.hpp \
+	./gecode/iter/ranges-inter.hpp ./gecode/iter/ranges-list.hpp ./gecode/iter/ranges-map.hpp \
+	./gecode/iter/ranges-minmax.hpp ./gecode/iter/ranges-minus.hpp ./gecode/iter/ranges-negative.hpp \
+	./gecode/iter/ranges-offset.hpp ./gecode/iter/ranges-operations.hpp ./gecode/iter/ranges-positive.hpp \
+	./gecode/iter/ranges-rangelist.hpp ./gecode/iter/ranges-scale.hpp ./gecode/iter/ranges-singleton-append.hpp \
+	./gecode/iter/ranges-singleton.hpp ./gecode/iter/ranges-size.hpp ./gecode/iter/ranges-union.hpp \
+	./gecode/iter/ranges-values.hpp ./gecode/iter/values-array.hpp ./gecode/iter/values-bitset.hpp \
+	./gecode/iter/values-bitsetoffset.hpp ./gecode/iter/values-inter.hpp ./gecode/iter/values-list.hpp \
+	./gecode/iter/values-map.hpp ./gecode/iter/values-minus.hpp ./gecode/iter/values-negative.hpp \
+	./gecode/iter/values-offset.hpp ./gecode/iter/values-positive.hpp ./gecode/iter/values-ranges.hpp \
+	./gecode/iter/values-singleton.hpp ./gecode/iter/values-union.hpp ./gecode/iter/values-unique.hpp \
+	./gecode/kernel.hh ./gecode/kernel/archive.hpp ./gecode/kernel/branch/action.hpp \
+	./gecode/kernel/branch/afc.hpp ./gecode/kernel/branch/chb.hpp ./gecode/kernel/branch/filter.hpp \
+	./gecode/kernel/branch/merit.hpp ./gecode/kernel/branch/print.hpp ./gecode/kernel/branch/tiebreak.hpp \
+	./gecode/kernel/branch/traits.hpp ./gecode/kernel/branch/val-commit.hpp ./gecode/kernel/branch/val-sel-commit.hpp \
+	./gecode/kernel/branch/val-sel.hpp ./gecode/kernel/branch/val.hpp ./gecode/kernel/branch/var.hpp \
+	./gecode/kernel/branch/view-sel.hpp ./gecode/kernel/branch/view-val.hpp ./gecode/kernel/branch/view.hpp \
+	./gecode/kernel/core.hpp ./gecode/kernel/data/array.hpp ./gecode/kernel/data/rnd.hpp \
+	./gecode/kernel/data/shared-array.hpp ./gecode/kernel/data/shared-data.hpp ./gecode/kernel/exception.hpp \
+	./gecode/kernel/gpi.hpp ./gecode/kernel/macros.hpp ./gecode/kernel/memory/allocators.hpp \
+	./gecode/kernel/memory/config.hpp ./gecode/kernel/memory/manager.hpp ./gecode/kernel/memory/region.hpp \
+	./gecode/kernel/modevent.hpp ./gecode/kernel/propagator/advisor.hpp ./gecode/kernel/propagator/pattern.hpp \
+	./gecode/kernel/propagator/subscribed.hpp ./gecode/kernel/propagator/wait.hpp ./gecode/kernel/range-list.hpp \
+	./gecode/kernel/shared-object.hpp ./gecode/kernel/shared-space-data.hpp ./gecode/kernel/trace/filter.hpp \
+	./gecode/kernel/trace/general.hpp ./gecode/kernel/trace/print.hpp ./gecode/kernel/trace/recorder.hpp \
+	./gecode/kernel/trace/tracer.hpp ./gecode/kernel/trace/traits.hpp ./gecode/kernel/var-imp.hpp \
+	./gecode/kernel/var-type.hpp ./gecode/kernel/var.hpp ./gecode/kernel/view.hpp \
+	./gecode/search.hh ./gecode/search/bab.hpp ./gecode/search/base.hpp \
+	./gecode/search/build.hpp ./gecode/search/cutoff.hpp ./gecode/search/dfs.hpp \
+	./gecode/search/engine.hpp ./gecode/search/exception.hpp ./gecode/search/lds.hpp \
+	./gecode/search/options.hpp ./gecode/search/pbs.hpp ./gecode/search/rbs.hpp \
+	./gecode/search/sebs.hpp ./gecode/search/seq/dead.hh ./gecode/search/statistics.hpp \
+	./gecode/search/stop.hpp ./gecode/search/support.hh ./gecode/search/trace-recorder.hpp \
+	./gecode/search/tracer.hpp ./gecode/search/traits.hpp ./gecode/support.hh \
+	./gecode/support/allocator.hpp ./gecode/support/auto-link.hpp ./gecode/support/bitset-base.hpp \
+	./gecode/support/bitset-offset.hpp ./gecode/support/bitset.hpp ./gecode/support/block-allocator.hpp \
+	./gecode/support/cast.hpp gecode/support/config.hpp ./gecode/support/dynamic-array.hpp \
+	./gecode/support/dynamic-queue.hpp ./gecode/support/dynamic-stack.hpp ./gecode/support/exception.hpp \
+	./gecode/support/failpoint.hpp ./gecode/support/hash.hpp ./gecode/support/heap.hpp \
+	./gecode/support/hw-rnd.hpp ./gecode/support/int-type.hpp ./gecode/support/macros.hpp \
+	./gecode/support/marked-pointer.hpp ./gecode/support/random.hpp ./gecode/support/ref-count.hpp \
+	./gecode/support/run-jobs.hpp ./gecode/support/sort.hpp ./gecode/support/static-stack.hpp \
+	./gecode/support/thread.hpp ./gecode/support/thread/thread.hpp ./gecode/support/timer.hpp \
+	./test/int.hh ./test/int.hpp ./test/test.hh \
+	./test/test.hpp

Makefile.in

@@ -337,7 +337,7 @@ INTSRC0 = \
 	bin-packing/conflict-graph.cpp \
 	order.cpp order/propagate.cpp \
 	unary.cpp cumulative.cpp cumulatives.cpp \
-	circuit.cpp no-overlap.cpp nvalues.cpp \
+	circuit.cpp no-overlap.cpp inter-distance.cpp nvalues.cpp \
 	member.cpp min-distance.cpp branch/action.cpp branch/chb.cpp \
 	arithmetic/mult.cpp  \
 	branch/view-sel.cpp branch/val-sel-commit.cpp \
@@ -427,7 +427,7 @@ INTHDR0 = \
 	circuit.hh circuit/base.hpp circuit/val.hpp circuit/dom.hpp \
 	no-overlap.hh no-overlap/dim.hpp no-overlap/box.hpp \
 	no-overlap/base.hpp no-overlap/man.hpp no-overlap/opt.hpp \
-	nvalues.hh nvalues/range-event.hpp \
+	inter-distance.hh nvalues.hh nvalues/range-event.hpp \
 	nvalues/sym-bit-matrix.hpp nvalues/graph.hpp \
 	nvalues/bool-base.hpp nvalues/bool-eq.hpp \
 	nvalues/bool-lq.hpp nvalues/bool-gq.hpp \
@@ -1121,7 +1121,7 @@ INTTESTSRC00 = \
 	rel linear gcc sorted unshare exec sequence \
 	mm-arithmetic mm-bool mm-lin mm-count mm-rel \
 	bin-packing order unary cumulative cumulatives circuit \
-	no-overlap precede nvalues member min-distance
+	no-overlap precede inter-distance nvalues member min-distance
 INTTESTSRC0 = test/int.cpp $(INTTESTSRC00:%=test/int/%.cpp)
 INTTESTOBJ = $(INTTESTSRC0:%.cpp=%$(OBJSUFFIX))
 

changelog.in

@@ -162,6 +162,21 @@ The propagation algorithms follow:
 M. Z. Lagerkvist, Propagation Algorithms for the Minimum-Distance Constraint
 over Selected Points, ModRef 2026.
 
+[ENTRY]
+Module: int
+What:   new
+Rank:   major
+[DESCRIPTION]
+Add the inter-distance constraint for fixed and variable separation. Basic
+propagation checks feasibility and bounds the distance; advanced propagation
+adds staged quadratic bounds filtering. The algorithms are described in:
+C.-G. Quimper, A. Lopez-Ortiz, G. Pesant, A Quadratic Propagator for the
+Inter-Distance Constraint, AAAI 2006, and Constraint Programming Letters 3
+(2008), 21-35.
+M. R. Garey, D. S. Johnson, B. B. Simons, R. E. Tarjan, Scheduling Unit-Time
+Tasks with Arbitrary Release Times and Deadlines, SIAM Journal on Computing
+10(2) (1981), 256-269.
+
 [RELEASE]
 Version: 6.4.0
 Date: 2026-07-15

cmake/GecodeSources.cmake

@@ -88,6 +88,7 @@ set(GECODE_INT_SOURCES
   gecode/int/extensional/tuple-set.cpp
   gecode/int/gcc.cpp
   gecode/int/int-set.cpp
+  gecode/int/inter-distance.cpp
   gecode/int/ldsb.cpp
   gecode/int/ldsb/sym-imp.cpp
   gecode/int/ldsb/sym-obj.cpp
@@ -415,6 +416,7 @@ set(GECODE_TEST_SOURCES
   test/int/exec.cpp
   test/int/extensional.cpp
   test/int/gcc.cpp
+  test/int/inter-distance.cpp
   test/int/linear.cpp
   test/int/member.cpp
   test/int/min-distance.cpp

gecode/int.hh

@@ -1748,6 +1748,75 @@ namespace Gecode {
   //@}
 
 
+  /**
+   * \defgroup TaskModelIntInterDistance Inter-distance constraint
+   * \ingroup TaskModelInt
+   */
+  //@{
+  /** \brief Post bounds-consistent propagator for \f$|x_i-x_j|\geq p\f$ for all \f$0\leq i\neq j<|x|\f$
+   *
+   * Domains with holes are treated as intervals between their bounds.
+   *
+   * - \a IPL_BASIC checks interval feasibility in \f$O(n\log n)\f$ time
+   *   and linear temporary space, where \f$n=|x|\f$.
+   * - \a IPL_ADVANCED and \a IPL_BASIC_ADVANCED first perform
+   *   the basic check, then schedule quadratic bounds(Z) filtering at
+   *   a higher cost. This filtering uses quadratic temporary space.
+   *
+   * The default, \a IPL_DEF, uses both stages. The value/bounds/domain part
+   * of \a ipl does not affect these algorithms.
+   *
+   * A zero distance, or fewer than two variables, imposes no restriction.
+   * A distance of one is propagated as a bounds-consistent distinct constraint.
+   *
+   * The propagator uses algorithms taken from:
+   *
+   * Claude-Guy Quimper, Alejandro Lopez-Ortiz, and Gilles Pesant,
+   * A Quadratic Propagator for the Inter-Distance Constraint,
+   * AAAI, pages 123-128, 2006.
+   *
+   * and
+   *
+   * M. R. Garey, D. S. Johnson, B. B. Simons, and R. E. Tarjan,
+   * Scheduling Unit-Time Tasks with Arbitrary Release Times and Deadlines,
+   * SIAM Journal on Computing 10(2), pages 256-269, 1981.
+   *
+   * Throws Int::OutOfLimits if \a p is negative or exceeds Int::Limits::max.
+   * Throws Int::ArgumentSame if \a p is positive and \a x contains the same
+   * unassigned variable multiply.
+   */
+  GECODE_INT_EXPORT void
+  inter_distance(Home home, const IntVarArgs& x, int p,
+                 IntPropLevel ipl=IPL_DEF);
+  /** \brief Post inter-distance constraint with variable separation
+   *
+   * Constrains \f$p\geq0\f$ and \f$|x_i-x_j|\geq p\f$ for all
+   * \f$0\leq i\neq j<|x|\f$.
+   *
+   * Uses the same algorithm options as the fixed-distance overload.
+   * The basic stage additionally tightens \a p's upper bound by binary
+   * search using the linear-space feasibility checker. Its time bound
+   * is \f$O(n\log n\log(1+\max(p)))\f$. The advanced stage provides
+   * bounds(Z) consistency for \a x using the minimum of \a p, giving
+   * bounds(Z) consistency for the whole constraint.
+   *
+   * The variable-distance algorithm is taken from:
+   *
+   * Claude-Guy Quimper, Alejandro Lopez-Ortiz, and Gilles Pesant,
+   * A Quadratic Propagator for the Inter-Distance Constraint,
+   * Constraint Programming Letters 3, pages 21-35, 2008, Section 5.
+   *
+   * Fewer than two variables only constrain \a p to be nonnegative.
+   * With at least two variables, throws Int::ArgumentSame if \a p is the
+   * same unassigned variable as a member of \a x, or if \a p can be positive
+   * and \a x contains the same unassigned variable multiply.
+   */
+  GECODE_INT_EXPORT void
+  inter_distance(Home home, const IntVarArgs& x, IntVar p,
+                 IntPropLevel ipl=IPL_DEF);
+  //@}
+
+
   /**
    * \defgroup TaskModelIntDistinct Distinct constraints
    * \ingroup TaskModelInt