If you were to define some extension methods, properties in an assembly written in F#, and then use that assembly in C#, would you see the defined extensions in C#?
Per the language spec, section 10.7 "Type extensions":
Optional extension members are syntactic sugar for static members. Uses of optional extension members elaborate to calls to static members with encoded names where the object is passed as the first argument. The encoding of names is not specified in this release of F# and is not compatible with C# encodings of C# extension members