(1...2).publisher.share() with `print`s.

debugging_shared_sequence.swift

let upstream = (1...2)
	.publisher
	.print("\tPre-share") // ⇐
	.share()
	.print("Post-share") // ⇐

let cancellable = upstream
	.first()
	.flatMap { first in
		upstream
			.prepend(first, first)
	}
	.pairwise()
	.sink(receiveValue: { _ in }) // Removing the `print` call to
	// focus in on the `Publisher.print`s, above.

// Outputs (without the annotations):
// ```
// Post-share: receive subscription: (Multicast) ⇒ Start of the `first` subscription.
// Post-share: request unlimited
// 	Pre-share: receive subscription: (1...2)
// 	Pre-share: request unlimited
// 	Pre-share: receive value: (1)
// Post-share: receive value: (1)
// Post-share: receive cancel
// Post-share: receive subscription: (Multicast) ⇒ The `flatMap`’d subscription.
// Post-share: request unlimited
// 	Pre-share: receive subscription: (1...2)
// 	Pre-share: request unlimited
// 	Pre-share: receive value: (1)
// Post-share: receive value: (1)
// 	Pre-share: receive value: (2)
// Post-share: receive value: (2)
// 	Pre-share: receive finished
// Post-share: receive finished ⇒ End of the `flatMap`’d subscription.
// 	Pre-share: receive value: (2) ⇒ The lingering `2` from the `first` subscription.
// 	Pre-share: receive finished ⇒ Finished event from the `first` subscription.
// ```