"FSLib" namespaces:

ref: lib/fslib/builtin.fs

"Microsoft.FSharp.Compatibility.CompatArray"

"Microsoft.FSharp.Compatibility.CompatMatrix"

"Microsoft.FSharp.Idioms"

"Microsoft.FSharp.Experimental.Reflection"

"Microsoft.FSharp.Math.BigNat" (since made private)

"Microsoft.FSharp.Math.BigInt"

"Microsoft.FSharp.Math.Rational"

also num (check sig)