Lattice Library
This enchantment enters with X study counters on it. When this enchantment enters and whenever you cast your first spell with {X} in its mana cost each turn, create a 0/0 green and blue Fractal creature token. Put a number of +1/+1 counters on it equal to the number of study counters on this enchantment.
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Official rulings (2) · Scryfall
If you cast your first spell with {X} in its mana cost during a turn before Lattice Library is on the battlefield (including Lattice Library itself), casting another spell with {X} in its mana cost later in the turn won't cause its last ability to trigger.
Lattice Library's last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack.