/// This trait should be used on all objects and containers related to storing unprotected terms, or unprotected symbols.
/// Should return true iff the given [ATermRef] is contained in the object. Used for runtime checks.
/// Should return true iff the given [SymbolRef] is contained in the object. Used for runtime checks.
// In Rust Its not yet possible to implement it for any tuples, so we implement it for some common sizes.