Insert the specified value into this map if a key (the first element) equivalent to that of value does not already exist in this map; otherwise, if a value_type object whose key is equivalent to that of value already exists in this map, this method has no effect. Return a pair whose first member is an iterator referring to the (possibly newly inserted) value_type object in this map whose key is equivalent to that of value, and whose second member is true if a new value was inserted, and false if the key was already present. This method requires that the (template parameter) types KEY and VALUE both be copy-insertable into this map (see {Requirements on KEY and VALUE}).