From c38c14b0b437f29e6e5e1b9b3cad2238d5c60791 Mon Sep 17 00:00:00 2001
From: Johannes Schmitt <schmitt@mathematik.uni-kl.de>
Date: Wed, 21 Aug 2024 15:59:17 +0200
Subject: [PATCH] Fix #4018

---
 src/Rings/mpoly-graded.jl |  4 ++--
 src/Rings/mpoly-ideals.jl |  2 +-
 src/Rings/mpoly.jl        |  8 ++++++--
 test/Rings/mpoly.jl       | 15 ++++++++++++---
 4 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/src/Rings/mpoly-graded.jl b/src/Rings/mpoly-graded.jl
index a1b1f6f4a727..4e6432bf3184 100644
--- a/src/Rings/mpoly-graded.jl
+++ b/src/Rings/mpoly-graded.jl
@@ -1502,8 +1502,8 @@ mutable struct HilbertData
     @req coefficient_ring(R) isa AbstractAlgebra.Field "The coefficient ring must be a field"
     @req all(is_homogeneous, gens(I)) "The generators of the ideal must be homogeneous"
 
-    G = groebner_assure(I)
-    cf = Singular.hilbert_series_data(G.S, W)
+    S = singular_groebner_generators(I, false, true)
+    cf = Singular.hilbert_series_data(S, W)
     return new(cf, W, I)
   end
   function HilbertData(B::IdealGens)
diff --git a/src/Rings/mpoly-ideals.jl b/src/Rings/mpoly-ideals.jl
index 2ac686fad008..fc3085415601 100644
--- a/src/Rings/mpoly-ideals.jl
+++ b/src/Rings/mpoly-ideals.jl
@@ -2112,7 +2112,7 @@ function grassmann_pluecker_ideal(ring::MPolyRing,
     return coeff_ring(numerator(c))
   end
   if !is_graded(ring)
-	 ring, _ = grade(ring)
+    ring, _ = grade(ring)
   end
   h = hom(base_ring(I), ring, coeffmap, gens(ring))
   converted_generators = elem_type(ring)[h(g) for g in groebner_basis(I; ordering = degrevlex(base_ring(I)))]
diff --git a/src/Rings/mpoly.jl b/src/Rings/mpoly.jl
index 75942e246997..f3e0bc3ce23f 100644
--- a/src/Rings/mpoly.jl
+++ b/src/Rings/mpoly.jl
@@ -383,7 +383,11 @@ function singular_generators(B::IdealGens, monorder::MonomialOrdering=default_or
   isdefined(B, :ord) && B.ord == monorder && monomial_ordering(B.Ox, Singular.ordering(base_ring(B.S))) == B.ord && return B.gens.S
   SR = singular_poly_ring(B.Ox, monorder)
   f = Singular.AlgebraHomomorphism(B.Sx, SR, gens(SR))
-  return Singular.map_ideal(f, B.gens.S)
+  S = Singular.map_ideal(f, B.gens.S)
+  if isdefined(B, :ord) && B.ord == monorder
+    S.isGB = B.isGB
+  end
+  return S
 end
 
 @doc raw"""
@@ -745,7 +749,7 @@ function singular_assure(I::IdealGens)
     I.gens.Sx = singular_poly_ring(I.Ox; keep_ordering = I.keep_ordering)
     I.gens.S = Singular.Ideal(I.Sx, elem_type(I.Sx)[I.Sx(x) for x = I.O])
   end
-  if I.isGB
+  if I.isGB && (!isdefined(I, :ord) || I.ord == monomial_ordering(I.gens.Ox, internal_ordering(I.gens.Sx)))
     I.gens.S.isGB = true
   end
 end
diff --git a/test/Rings/mpoly.jl b/test/Rings/mpoly.jl
index e37ecce6ca33..cfd420f78912 100644
--- a/test/Rings/mpoly.jl
+++ b/test/Rings/mpoly.jl
@@ -300,9 +300,18 @@ end
 end
 
 @testset "Grassmann Plücker Relations" begin
-    R, x = graded_polynomial_ring(residue_ring(ZZ, 7)[1], "x" => (1:2, 1:3))
-    test_ideal =ideal([x[1, 2]*x[2, 2] + 6*x[2, 1]*x[1, 3] + x[1, 1]*x[2, 3]])
-    @test grassmann_pluecker_ideal(R, 2, 4) == test_ideal
+  R, x = graded_polynomial_ring(residue_ring(ZZ, 7)[1], "x" => (1:2, 1:3))
+  test_ideal =ideal([x[1, 2]*x[2, 2] + 6*x[2, 1]*x[1, 3] + x[1, 1]*x[2, 3]])
+  @test grassmann_pluecker_ideal(R, 2, 4) == test_ideal
+
+  # Issue #4018
+  I = grassmann_pluecker_ideal(2, 5)
+  @test degree(I) == 5
+  @test dim(I) == 7
+  R, x = graded_polynomial_ring(GF(7), 10, "x")
+  I = grassmann_pluecker_ideal(R, 2, 5)
+  @test degree(I) == 5
+  @test dim(I) == 7
 end
 
 @testset "IdealGens" begin