Julien hadn't really been thinking about much other than Alfie after his last meeting with the other boy, even while he studied his new pet project. He was still spinning the plates of his current year homework for the spring term as well as work on next year's texts and berating himself for doing so badly on those, but while an idea had a hold of his mind he'd come to realise there was no point in trying to ignore it. The theory, hypothesis, problem, whatever would need to be worked on or he'd just end up focusing on it entirely and forgoing everything else.
For a problem that was quite serious (indeed, potentially fatal) and so long-standing, the solution was not as simple as it once seemed. Julien was beginning to see why the stairs had gone so long without this kind of protection - the factors that needed to be taken into account were great and he'd found out that he'd need to study the staircases movements themselves as well as spells that worked around gravity and force and inertia.
It was hard going but he thought he'd come across a book mentioned in another bibliography that should be able to help him with a different perspective, reversing the gravitational pull so that a body would fall up instead of down, thereby not just creating another hard surace to land on; his ribs ached in phantom pain remembering that.
He was busy looking up at the stacks, rows of books above his head, so he didn't see the Gryffindor reaching for the same book until it was too late and he was halfway through an 'Accio'. He managed half the title of the book he'd wanted, which meant that half the shelf came at them both, narrowly deflected by a hastily thrown shield charm.
And he still managed to apologise while it was happening.