//------------------------------//
// Puzzle 19: Double Vision, Part 1 
// Story: School of Logic: a Collection of Puzzles involving the Student Six 
// by Coyotek4 
//------------------------------//

Daylight shines through the window, a natural alarm clock for Sandbar as he rises from his bed and goes through his daily before-school routine.

Entering the kitchen area, Sandbar mumbles greetings to his fellow non-pony students. “Mornin’, Silverstream. Mornin’, Yona, Mornin’, Gallus. Mornin’, Silverstream. Mornin’ …”

His eyelids snap open as a realization hits him. He turns around to see a giggling Silverstream, then back to his front to eye the hippogriff chuckling at him.

“What gives?” he suddenly bellows, as all around him his friends break out into laughter … soon causing Sandbar himself to join in.

“It’s a challenge,” the Silverstream in front of him states. “Can you figure out which Silverstream is me, and which one is … oh wait … shoot!.” This Silverstream smacks her head with a claw as the other one flutters over to her.

“Don’t worry about it,” the other hippogriff states before emanating a flash; an instant later, Ocellus hovers next to her friend.

“I meant to say ‘which one of us is Silverstream’,” the ‘real’ Silverstream notes.

“Don’t sweat it, that wasn’t the test anyway,” Ocellus replies.

“Test? What test?” Sandbar asks.

“You said you wanted a chance to prove your mental acuity, right?” Gallus states.

“Wait, you’re saying Sandbar cute? Don’t we all know that?” Yona asks, causing the griffon to suppress a laugh.

“He means Ocellus created a challenge for Sandbar … well, several challenges, I guess,” Smolder corrects.

Sandbar turns to Ocellus. “What about those ‘ordering tests’ you mentioned last night?”

Ocellus blushes. “I just couldn’t think of anything to come up with that we hadn’t already done. And believe me, I thought about those tests for hours … but it occurred to me that I could create a whole new test for you, based on a test that Thorax gave our professors.”

“Wait,” Silverstream interrupts, “our professors were given tests?”

“Thorax told me about a ‘Spot the Changeling’ challenge he did, where he would pick one of the six ponies and take her place; the others had to figure out which of them was Thorax in disguise.”

“Couldn’t they just ask each other questions that only the professors would know?” Gallus dryly asks.

“They put conditions in to prevent that. In any case, I thought we could do that, but on a smaller and more logic-based scale.”

Ocellus flutters out to the foyer, returning with the deck of ‘Mind’ cards from the previous night. She quickly searches the deck, pulling out four cards: the 1, 2, 3, and 4.

“Here’s how this will work,” Ocellus starts. “You’ll close your eyes, and when you open them you’ll see two Silverstreams, one of which will be me. Each of us will make a number of statements, and then you have to figure out which of us is Silverstream and which of us is me, Ocellus.”

“Seems simple,” Sandbar says, “but what’s with the cards?”

“This is where the ‘logic’ part comes in. Each of us will have one of these cards in front of us. Any statement made by somecreature with an even-numbered card in front of her will be true, and any statement made by somecreature with an odd-numbered card in front of her will be false. In other words, having the 2 or 4 means true statements and having the 1 or 3 means false statements. And you have to figure out which card we each have as well.”

“Whoa … that sounds a lot harder,” Sandbar notes.

“We’ll do five rounds … let’s see how you do. Ready?”

Sandbar closes his eyes. “Ready.”

Ocellus turns to Silverstream. “Are you ready?”

“I hope so,” the hippogriff says somewhat apprehensively. “I did try to remember what you told me to say.”

Ocellus smiles. “You’ll do fine,” she assures her friend.

The sole pony’s eyes now shut, Ocellus changes her appearance to mimic that of her hippogriff friends. Each takes a card, and the rounds begin:

[In each round, one Silverstream appears on Sandbar’s left (L) and one appears on his right (R).]



[Round 1]
L: “I am Silverstream. I have the 1.”
R: “I am Ocellus. I have the 2.”





[Round 2]
L: “I am Silverstream. I do not have the 3.”
R: “I am Ocellus. I do not have the 4.”





[Round 3]
L: “I am Silverstream. Both of us have even-numbered cards.”
R: “I am Silverstream. My card’s number is the smaller of the two.”





[Round 4]
L: “Either I am Silverstream or I have the 1.”
R: “Ocellus has the 1. Neither of us has the 4.”





[Round 5]
L: “Either Silverstream has the 1 or Ocellus has the 3. Neither of us has the 2.”
R: “Either Silverstream has the 3 or Ocellus has the 4. Neither of us has the 1.”