func subSequenceIndexBug
    <C: Collection
    where
    C.Iterator.Element: Equatable,
    C.SubSequence: Collection,
    C.SubSequence.Index == C.Index,
    C.SubSequence.Iterator.Element == C.Iterator.Element>
    (_ c: C, _ e: C.Iterator.Element)
{
    let junction = c.index(c.startIndex, offsetBy: numericCast(5)) // Arbitrary split point.   
    if let i = c.suffix(from: junction).index(of: e) {
        print("Searched for \"\(e)\" and found \"\(c[i])\". Result of testing them for equality is: \(e == c[i])")
    }
}

subSequenceIndexBug("ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters, "Q")
// Prints: "Searched for "Q" and found "L". Result of testing them for equality is: false"