diff --git a/src/library/function/term.jl b/src/library/function/term.jl
index c12755c..5230a29 100644
--- a/src/library/function/term.jl
+++ b/src/library/function/term.jl
@@ -59,15 +59,15 @@ function varlt(u::Term{V}, v::Term{V}) where {V}
 end
 
 function varmul(u::Term{V}, v::Term{V}) where {V}
-    return Term{V}(sortedmergewith(u.ω, v.ω))
+    return Term{V}(sortedmergewith(u.ω, v.ω; lt = varlt))
 end
 
 function varmul(u::Term{V}, v::V) where {V}
-    return Term{V}(sortedmergewith(u.ω, V[v]))
+    return Term{V}(sortedmergewith(u.ω, V[v]; lt = varlt))
 end
 
 function varmul(u::V, v::Term{V}) where {V}
-    return Term{V}(sortedmergewith(V[u], v.ω))
+    return Term{V}(sortedmergewith(V[u], v.ω; lt = varlt))
 end
 
 function varmul(u::V, v::V) where {V}
diff --git a/test/assets/assets.jl b/test/assets/assets.jl
index a8adcb0..522c491 100644
--- a/test/assets/assets.jl
+++ b/test/assets/assets.jl
@@ -53,10 +53,14 @@ end
 
 const VI = VariableIndex
 
-function PBO.varlt(u::VariableIndex, v::VariableIndex)::Bool
+function PBO.varlt(u::VariableIndex, v::VariableIndex)
     return PBO.varlt(u.index, v.index)
 end
 
+function PBO.varshow(v::VariableIndex)
+    return PBO.varshow(v.index)
+end
+
 # Test foreign packages
 function run_foreign_pkg_tests(pkg_name::AbstractString, dep_path::AbstractString = PBO.__PROJECT__; kws...)
     @info "Running Tests for '$pkg_name'"
diff --git a/test/integration/interface.jl b/test/integration/interface.jl
index a5f4090..97923d3 100644
--- a/test/integration/interface.jl
+++ b/test/integration/interface.jl
@@ -15,6 +15,40 @@ function test_variable_interface()
             @test PBO.varlt(VI(1), VI(-1)) === true
             @test PBO.varlt(VI(-1), VI(1)) === false
             @test PBO.varlt(VI(-1), VI(-1)) === false
+
+            @test PBO.Term([VI(4), VI(2), VI(1), VI(2), VI(4)]) == PBO.Term{VI}([VI(1), VI(2), VI(4)])
+        end
+
+        @testset "varshow" begin
+            @test PBO.varshow(VI(101)) == "x₁₀₁"
+            @test PBO.varshow(VI(-12)) == "x₋₁₂"
+
+            @test PBO.varshow(PBO.Term([VI(1), VI(2), VI(4)])) == "x₁ x₂ x₄"
+        end
+
+        @testset "varmul" begin
+            let x = VI(1)
+                y = VI(2)
+                z = VI(3)
+
+                let xy = PBO.Term([x, y])
+                    xz = PBO.Term([x, z])
+                    yz = PBO.Term([y, z])
+
+                    @test PBO.varmul(x, y) == xy
+                    @test PBO.varmul(y, x) == xy
+
+                    @test PBO.varmul(x, z) == xz
+                    @test PBO.varmul(z, x) == xz
+
+                    @test PBO.varmul(y, z) == yz
+                    @test PBO.varmul(z, y) == yz
+
+                    @test PBO.varmul(xy, z) == PBO.Term([x, y, z])
+                    @test PBO.varmul(xz, y) == PBO.Term([x, y, z])
+                    @test PBO.varmul(x, yz) == PBO.Term([x, y, z])
+                end
+            end
         end
     end