| FlatMapAsync(FuncTaskRes) | 
            (async version) 
            Returns the error when IsErr; map() when IsOk, flattenning the result.
            This is a shorthand for sequential Map and Flatten calls.
             C#  | 
| FlatMapAsyncTOut(FuncTaskResTOut) | 
            (async version) 
            Returns the error when IsErr; map() when IsOk, flattenning the result.
            This is a shorthand for sequential Map and Flatten calls.
             C#  |