prog.cs(10,28): error CS1061: Type `System.Collections.Hashtable' does not contain a definition for `keys' and no extension method `keys' of type `System.Collections.Hashtable' could be found. Are you missing an assembly reference?
/usr/lib/mono/4.5/mscorlib.dll (Location of the symbol related to previous error)
Compilation failed: 1 error(s), 0 warnings