From 146087011bdd6af8e9569ca9dd0f142f63713751 Mon Sep 17 00:00:00 2001
From: Mahrud Sayrafi <mahrud@berkeley.edu>
Date: Thu, 5 Jun 2025 18:26:51 -0400
Subject: [PATCH] changed how complexes are checked to be identical internally

---
 .../packages/Complexes/ChainComplex.m2        |  8 +++++--
 .../packages/Complexes/ChainComplexMap.m2     | 23 +++++++++++++------
 .../packages/Complexes/ChainComplexTests.m2   | 10 ++++++++
 3 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/M2/Macaulay2/packages/Complexes/ChainComplex.m2 b/M2/Macaulay2/packages/Complexes/ChainComplex.m2
index 82a5b4595ef..5989e468490 100644
--- a/M2/Macaulay2/packages/Complexes/ChainComplex.m2
+++ b/M2/Macaulay2/packages/Complexes/ChainComplex.m2
@@ -280,8 +280,12 @@ length Complex := (C) -> (
     hi-lo
     )
 
-Complex == Complex := (C,D) -> (
-    if C === D then return true;
+-- this method is not exported, and is only used internally instead of === and =!=,
+-- since Complex is a MutableHashTable and are never identical unless literally the same.
+isIdentical = method()
+isIdentical(Complex, Complex) := (C, D) -> C === D or C.module === D.module and C.dd.map === D.dd.map
+
+Complex == Complex := (C,D) -> isIdentical(C, D) or (
     (loC,hiC) := C.concentration;
     (loD,hiD) := D.concentration;
     if ring C =!= ring D then return false;
diff --git a/M2/Macaulay2/packages/Complexes/ChainComplexMap.m2 b/M2/Macaulay2/packages/Complexes/ChainComplexMap.m2
index 08625c4a0dc..4ca93d1058c 100644
--- a/M2/Macaulay2/packages/Complexes/ChainComplexMap.m2
+++ b/M2/Macaulay2/packages/Complexes/ChainComplexMap.m2
@@ -110,7 +110,7 @@ map(Complex, Complex, ComplexMap) := ComplexMap => opts -> (tar, src, f) -> (
     )
 
 ComplexMap | ComplexMap := ComplexMap => (f,g) -> (
-    if target f =!= target g then error "expected targets to be the same";
+    if not isIdentical(target f, target g) then error "expected targets to be the same";
     deg := degree f;
     if deg =!= degree g then error "expected maps with the same degree";
     result := map(target f, source f ++ source g, {{f,g}}, Degree=>deg);
@@ -121,7 +121,7 @@ ComplexMap | ComplexMap := ComplexMap => (f,g) -> (
     )
 
 ComplexMap || ComplexMap := ComplexMap => (f,g) -> (
-    if source f =!= source g then error "expected sources to be the same";
+    if not isIdentical(source f, source g) then error "expected sources to be the same";
     deg := degree f;
     if deg =!= degree g then error "expected maps with the same degree";
     result := map(target f ++ target g, source f, {{f},{g}}, Degree=>deg);
@@ -277,8 +277,14 @@ ComplexMap ^ ZZ := ComplexMap => (f,n) -> (
       )
   )
 
-ComplexMap == ComplexMap := (f,g) -> (
-    if f === g then return true;    
+-- this method is not exported, and is only
+-- used internally instead of === and =!=
+isIdentical(ComplexMap, ComplexMap) := (f, g) -> f === g or (
+    f.degree === g.degree and f.map === g.map
+    and isIdentical(f.source, g.source)
+    and isIdentical(f.target, g.target))
+
+ComplexMap == ComplexMap := (f,g) -> isIdentical(f, g) or (
     if source f != source g or target f != target g 
       then return false;
     (lo1,hi1) := (source f).concentration;
@@ -524,7 +530,8 @@ truncate(ZZ,   ComplexMap) :=
 truncate(List, ComplexMap) := ComplexMap => truncateMatrixOpts >> opts -> (degs, f) -> (
     d := degree f;
     C := truncate(degs, source f, opts);
-    D := if source f === target f then C else truncate(degs, target f, opts);
+    D := if isIdentical(source f, target f) then C
+    else truncate(degs, target f, opts);
     map(D, C, i -> inducedTruncationMap(D_(i+d), C_i, f_i), Degree => d))
 
 --------------------------------------------------------------------
@@ -538,7 +545,8 @@ basis(ZZ,   ComplexMap) :=
 basis(List, ComplexMap) := ComplexMap => opts -> (deg, f) -> (
     d := degree f;
     C := basis(deg, source f, opts);
-    D := if source f === target f then C else basis(deg, target f, opts);
+    D := if isIdentical(source f, target f) then C
+    else basis(deg, target f, opts);
     map(D, C, i -> inducedBasisMap(D_(i+d), C_i, f_i), Degree => d))
 
 --------------------------------------------------------------------
@@ -1276,7 +1284,8 @@ liftMapAlongQuasiIsomorphism(ComplexMap, ComplexMap) := (alpha,beta) -> (
     P := source alpha;
     N := target alpha;
     M := source beta;
-    if N =!= target beta then error "expected targets of two maps to be the same complex";
+    if not isIdentical(N, target beta)
+    then error "expected targets of two maps to be the same complex";
     (loP, hiP) := concentration P;
     Cbeta := cone beta;
     gamma := new MutableHashTable;
diff --git a/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2 b/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2
index 484acfc3389..388aed68bd3 100644
--- a/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2
+++ b/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2
@@ -341,6 +341,16 @@ TEST ///
   assert isWellDefined C
   assert(HH C != complex coker f0)
   assert(prune HH C == complex coker f0)
+
+  C = complex R
+  D = complex R
+  assert(C == D)
+  assert(C =!= D)
+  -- these operations didn't work before isIdentical
+  -- was used internally instead of === and =!=
+  id_C | id_D
+  id_C || id_D
+  id_C // id_D
 ///
 
 TEST ///