io.Readerで先頭Nバイトを読み捨てる

package main

import (
    "io"
    "io/ioutil"
    "strings"
    "os"
)

func main() {
    a := strings.NewReader("123456789")
    r := io.LimitReader(a, 5)
    t := io.TeeReader(r, ioutil.Discard)
    io.ReadAll(t)
 
    io.Copy(os.Stdout, a) // 6789
}