Fix in for ExponentsIterator

src/comparison.jl

@@ -513,6 +513,23 @@ end
 
 nvariables(it::ExponentsIterator) = length(it.object)
 
+function Base.in(x, it::ExponentsIterator)
+    if length(x) != nvariables(it)
+        return false
+    end
+    if any(xi -> xi < 0, x)
+        return false
+    end
+    deg = sum(x)
+    if deg < it.mindegree
+        return false
+    end
+    if it.maxdegree !== nothing && deg > it.maxdegree
+        return false
+    end
+    return true
+end
+
 _last_lex_index(n, ::Type{LexOrder}) = n
 _prev_lex_index(i, ::Type{LexOrder}) = i - 1
 _not_first_indices(n, ::Type{LexOrder}) = n:-1:2

test/comparison.jl

@@ -26,6 +26,21 @@ function test_equal()
     @test exp != ExponentsIterator{LexOrder}([0], maxdegree = 2)
 end
 
+function test_in()
+    # Unbounded iterator (no maxdegree)
+    it = ExponentsIterator{Graded{LexOrder}}([0, 0])
+    @test [0, 0] in it
+    @test [1, 2] in it
+    @test [3] ∉ it          # wrong number of variables
+    @test [0, 0, 0] ∉ it   # wrong number of variables
+    # Bounded iterator
+    it2 = ExponentsIterator{LexOrder}([0, 0], mindegree = 1, maxdegree = 3)
+    @test [1, 0] in it2
+    @test [1, 2] in it2
+    @test [0, 0] ∉ it2     # degree too low
+    @test [2, 2] ∉ it2     # degree too high
+end
+
 function test_errors()
     err = ArgumentError(
         "The `mindegree` of `ExponentsIterator` cannot be negative.",