Remove a book from a library and it stands still the same.
Remove another and one more, and onwards in this way.
How long can you continue, for how many days,
Before no library is before you, and the concept starts to fray?

Now take the man before you, what he is is made through change.
What is it within him that makes past and future the same?
The body has continued, though clearly grown and aged.
Who he is now is content, your idea of him a frame.

His mind is still his own, though it has turned the page.
"Cogito ergo sum" the old Cartesian phrase.
How he thought before can be said as but a phase
And how he thinks is who he is. The man stood here has changed.

But still there's keen resemblance that you're clearly keen to hold.
Is he the same man young, as he'll be when he is old?