CodeDom Compiler: Which assemblies are referenced by default?

Question

Short: Which assemblies (Framework DLLs) are included by default in .NET CodeDom Compilers (CSharpCodeProvider or VBCodeProvider) without explicitely adding the reference to CompilerParameters?

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I am using the CodeDom tools, namely CSharpCodeProvider and VBCodeProvider, to compile assemblies at runtime. I noticed, that some but not all .NET reference assemblies are included by default.

I can use everything in System.dll without adding the reference in the CompilerParameters but nothing from System.Numerics.dll for example. For the latter I need to add params.ReferencedAssemblies.Add("System.Numerics.dll") to my code.

Hence my question: How do I know, which assemblies are referenced by default, and which are not?

Relevant code:

This code can be compiled without added references:

Imports System
Public Class Foo
    Public Sub TestClass
        Dim t = Tuple.Create(23,241)
    End Sub
End Class

This code can not:

Imports System
Imports System.Numerics
Public Class Foo
    Public Sub TestClass
        Dim t = Tuple.Create(23,241)
        Dim n As New Complex(32,112)
    End Sub
End Class

The code I use to compile (abbreviated):

Dim params As New CompilerParameters()
'The path of the assembly to create
params.OutputAssembly = active.OutputName

'Compile as dll
params.GenerateExecutable = False

Dim vb As New VBCodeProvider
Dim res = vb.CompileAssemblyFromSource(params, active.Code)