You have not cast an instant or sorcery this turn.
({4} magic symbol) ({U} magic symbol) ({U} magic symbol) on each odd-numbered turn, with at most ({3} magic symbol) ({U} magic symbol) available each even-numbered turn available.
Steps
Cast Walk the Aeons by paying ({4} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Chandra triggers, copying Walk the Aeons.
Resolve both Walk the Aeonss, causing you to take two extra turns after this one.
Move to your next turn.
Cast etiher Mystic Retrieval or Call to Mind by paying its mana cost, targeting either Call to Mind or Mystic Retrieval in your graveyard.
Chandra triggers, copying Call to Mind or Mystic Retrieval, targeting Walk the Aeons.
Resolve both Call to Minds or Mystic Retrievals, returning Walk the Aeons and either Call to Mind or Mystic Retrieval from your graveyard to your hand.
Move to your next turn.
Repeat.
Results
Infinite turns.
2 Instant/Sorcery with "Return Instant/Sorcery from GY to hand".