func Inner(str, head, tail string) string {

if head == "tail" {

return ""

}

i0, i1 := 0, 0

if head != "" {

i := strings.IndexFunc(str, func(r rune) bool {

if r == []rune(head)[0] {

return true

}

return false

})

i0 = i + 1

}

if tail != "" {

i := strings.IndexFunc(str, func(r rune) bool {

if r == []rune(tail)[0] {

return true

}

return false

})

i1 = i

if i1 == -1 {

i1 = len([]rune(str))

}

} else {

i1 = len([]rune(str))

}

return str[i0:i1]

}