Concept definition

    template<typename I, typename S = I>
    concept bidirectional_iterator =
    forward_iterator<I, S> && requires(I it) {
        { --it } -> std::same_as<I &>;
        { it-- } -> std::convertible_to<I>;
    }

Detailed Description

Concept for iterators supporting bidirectional traversal.

Refines forward_iterator, adding support for reverse movement using –it and it–.
Allows both pre-decrement and post-decrement operations, enabling traversal in both forward and backward directions.
An optional sentinel type S can be provided to check range consistency between begin() and end().

Template Parameters

I	Iterator-like type supporting bidirectional movement.
S	Sentinel type used to verify consistency (defaults to `I`).