Subclause 
[tuple] describes the tuple library that provides a tuple type as
the class template 
tuple that can be instantiated with any number
of arguments
.Each template argument specifies
the type of an element in the 
tuple.Consequently, tuples are
heterogeneous, fixed-size collections of values
.An instantiation of 
tuple with
two arguments is similar to an instantiation of 
pair with the same two arguments
.