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--- sage.cpp.orig 2021-01-24 16:21:00 UTC
+++ sage.cpp
@@ -0,0 +1,60 @@
+/*
+ Coxeter version 3.0 Copyright (C) 2009 Mike Hansen
+ See file main.cpp for full copyright notice
+
+ Patch from Jeroen Demeyer <jdemeyer@cage.ugent.be>,
+ borrowed by SageMath: Add Sage interface.
+
+*/
+
+#include "sage.h"
+
+namespace sage {
+
+ void interval(List<CoxWord>& list, CoxGroup& W, const CoxWord& g, const CoxWord& h)
+
+ /*
+ Returns a list of the elements in the Bruhat interval between g and h.
+ Note that this assumes that g and h are in order.
+ */
+ {
+ if (not W.inOrder(g,h)) {
+ return;
+ }
+
+ W.extendContext(h);
+
+ CoxNbr x = W.contextNumber(g);
+ CoxNbr y = W.contextNumber(h);
+
+ BitMap b(W.contextSize());
+ W.extractClosure(b,y);
+
+ BitMap::ReverseIterator b_rend = b.rend();
+ List<CoxNbr> res(0);
+
+ for (BitMap::ReverseIterator i = b.rbegin(); i != b_rend; ++i)
+ if (not W.inOrder(x,*i)) {
+ BitMap bi(W.contextSize());
+ W.extractClosure(bi,*i);
+ CoxNbr z = *i; // andnot will invalidate iterator
+ b.andnot(bi);
+ b.setBit(z); // otherwise the decrement will not be correct
+ } else
+ res.append(*i);
+
+ schubert::NFCompare nfc(W.schubert(),W.ordering());
+ Permutation a(res.size());
+ sortI(res,nfc,a);
+
+ list.setSize(0);
+ for (size_t j = 0; j < res.size(); ++j) {
+ CoxWord w(0);
+ W.schubert().append(w, res[a[j]]);
+ list.append(w);
+ }
+
+ return;
+ }
+
+}
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