let a = AnySequence( [(1, 1), (3, 3), (5, 5), (7, 7)] )
let b = AnySequence( [(2, 2), (4, 4), (6, 6), (8, 8)] )

let c = [a, b]
    .joined()
    .map({ $0 })

// Playground execution failed:
//
// error: scratchpad.playground:6:10: error: cannot convert value of type '(_) -> _'
//        to expected argument type '(((Int, Int))) -> _'
// .map({ $0 })
// ^~~~~~

print(c)

let c = [a, b]
    .joined()
    .map({ arg in
        return arg
    })