Is expiation incumbent upon someone who swore not to memorize certain material, then proceeded to memorize it after finding summaries of it?

If your intention when swearing the oath was never to memorize the law material at all, then you have broken your oath and must offer expiation for breaking an oath. However, if your intention was not to memorize the long, difficult text, and then you found a short, easy text and memorized it, then no expiation is due from you, because the oath is based on the intention of the one who swears it. If the reason for the oath was the length and difficulty of the text, and then you found a short, easy text and memorized it, then no expiation is due from you.