http://archive.heinessen.com/mlp/thread/16499413#p16686294

"Let's see… It'd be… 60°, right?" Bundle Joy rolled her eyes as she saw the disapproving look on her master's face. "I mean τ/6 radians, of course. ∠PQR is τ/6 radians."

Dr. Diffy Q's expression brightened considerably, and he tossed BunBun a sugar cube. "Correct!" he affirmed with a nod. "You're making great progress. And I know it's a difficult adjustment, but in the long run you'll find radians make many things much simpler."

BunBun gobbled up the treat immediately. Already pregnant with sextuplets, she wasn't too worried about the possibility of ingesting a fertility drug. When she'd first become Doctor Q's broodfilly, the last thing she'd expected had been daily tutoring sessions. However, he'd insisted, going on about how math was the language of the universe, and revealed the underlying harmony, and she'd pretty much tuned out by the time he'd started rambling about installing an appreciation of the beauty of pure mathematics.

A satisfied smile appeared on Diffy's face and he scooted over to BunBun, resting his head against her swollen belly. "I think that's enough for today. How are our little buns in the oven doing?" he asked as he ran his hoof across the mound of her belly. She looked at least 6 months pregnant, though she had only been pregnant for half that long.

Bundle Joy looked down at his administrations and focused her mind inwards, probing the special connection her talent gave her with her unborn foals. "They're healthy. They don't seem to feel too crowded at the moment." She paused, licking her lips. "They seem to want fruit. Do you have any honeydew?"

Diffy nodded. "Womb service coming right up!" He lit his horn and a fresh fruit platter floated down from a hole in the ceiling, which she graciously snatched up.

"Thank you, Master!" she said through a mouthful of honeydew and strawberries.

Diffy just smiled as he watched his beautiful broodfilly munch away at a generous helping of miscellaneous fruits. He felt a swelling of pride as he admired her maternal form. Nestled comfortably in her young womb were a half dozen developing foals, HIS foals. And they were only the first. Pregnancy would become the norm for her. He had inseminated her every day since abducting her, usually in the evening, and would continue to do so for the rest of his life, after which his son would inherit her.

Bundle Joy savored the succulent flavors of the cantaloupe in her mouth. She had grown accustomed to her leash and collar, which weren't usually kept taut. She'd put her hair back in a bun, which suited her, and also kept it out of the way when she ate. She felt the slight fluttering of the life within her and giggled, finding herself enjoying her new life as a broodfilly more than she'd care to admit.

Doctor Q stood up and smiled. "Well, Bunny, I have a surprise for you."

Bundle Joy raised an eyebrow. "Oh? What is it?"

Diffy just chuckled and lit his horn. "You do know what 'surprise' means, right?" As he spoke, a polished wooden sawhorse rose from the floor, the top wrapped in a very soft cushion.

BunBun knew what she was to do. She got up and walked over to straddle it, her belly nestling into an expandable plush bowl, allowing her chest to rest on the horizontal beam. She moved her hooves close together and Dr. Q securely strapped them into place. It was a redundant show of dominance, but one he often insisted on, so she acquiesced.

Diffy smiled and lit his horn, floating a blindfold over her eyes. There was a long pause, and then she heard a new, smaller set of hoofsteps approaching. Then Diffy spoke. "Okay, son, she's yours for the taking. Just be careful not to bang her up too badly; she's carrying my foals."

Wait, "son"? Gears started turning in her head, and she remembered a comment her master had made after her first insemination.

"I, uh… okay. Are you sure about this, Dad? This doesn't feel right to me."

Diffy sighed. "Antiderivative, you're growing into a stallion now, and sooner or later you'll find a mare of your own. That's why I brought you here to teach you how to treat a mare."

Bundle Joy spoke timidly. "A-Antiderivative?"

There was the sound of hoofsteps approaching, and Antiderivative spoke. "Bundle Joy? I was wondering why you didn't show up for class. Look, I know I've said it a million times, but I'm sorry for what I did on the playground. I don't know what came over me; I just–"

"That's enough!" said Diffy Q's irritated voice. "Look, Anti, you have nothing to feel guilty about. You asserted your dominance over this young mare and brought two beautiful foals into the world. Are you really prepared to tell those poor colts you wish they didn't exist?"

"No, I–"

Doctor Q wasn't done. "No, you need to learn that there's nothing wrong with what you did; it was perfectly natural, and nothing to be ashamed of. Now rut that filly and remind her what her place is."

Bundle Joy heard the smaller set of hoofsteps get closer, and felt hooves on her shoulders as Anti began to mount her.

Antiderivative grunted as he rubbed his sheath up and down through the slit of the bound filly's marehood. Neither of them were particularly aroused, but he knew he had to properly penetrate her for his father to be satisfied.

BunBun whimpered as she felt the colt's member swell up, peaking out of its shaft. It slid along her netherlips like a hotdog in a bun, and poked at her cervix. She found herself getting moist from the physical stimulation, while her mind was telling her she shouldn't be enjoying this. This was the colt who had raped her as an even younger filly, and now his father, her new master, was forcing him to rape her again. But on another level, it felt good to be intimate with somepony her age for a change.

Doctor Q smiled with pride and accomplishment at the scene before her. As he'd expected, his son had gotten over his initial reluctance and was positioning the tip of his now fully erect horsecock at the broodfilly's marehood. Diffy watched as his son plunged his length all the way into the bound filly in a slow, smooth motion, only stopping once he had hilted inside her.

Antiderivative moaned as he started thrusting, savoring the wet warmth enveloping his colthood. The only previous time he'd had sex had been in the haze of a pheromone-induced lustful frenzy, so this was an entirely new experience. Now that he was in the moment, he could feel every ripple of her tight cunt as it massaged his cock, bringing him ever closer to a climax. As he blissfully fucked the helpless filly underneath him, Antiderivative realized how silly it was to be ashamed of himself over something so natural, and so pleasurable on such a primal level. As he picked up the pace, he resolved to find a broodfilly he could call his own, one who would carry his seed one way or another.

Bundle Joy shuddered as the colt started thrusting faster. His balls drew up, and she felt his thrusts become erratic. Her mind flashed back to just over a year ago, pinned in place by the same colt's magical aura. He had rutted her mercilessly, singularly focused on inseminating her as quickly as possible, in ensuring she would have to carry the fruits of his conquest for almost a year. It had only been a year, but she felt much older than she had been at the time.

Antiderivative threw his head back and shot his cum deep inside of her. He knew intellectually that she was already carrying his father's foals, and her special talent made the depth of insemination irrelevant, but the primal part of his brain told him to get as deep as possible to maximize the chance of conception. He lay on top of her for some time, pumping his pollen into her, grateful to his father for helping him to see the light.

Diffy Q smiled as he watched his son collapse on top of Bundle Joy, panting to catch his breath. He lay on her back as his member softened and shrunk, smiling contently. "That was pretty good for what was effectively your first time, Anti. With practice, you'll be able to hold out for much longer. So, what did you think?"

Antiderivative took a few deep breaths as he waited for his colthood to fully retract before dismounting, dribbling a line of cum onto the smooth matte-black floor. "To be honest, that felt really good. I wasn't sure at first because I'd heard it was wrong, but I just… it felt so RIGHT, Dad. I was so in control. I felt so powerful, and I… frankly, I'm a little jealous that you gave her three times as many foals in one go."

Diffy chuckled. "Well, she's a bit older now, and I cheated a bit." He winked at BunBun, who just quivered and stared blankly. "Anyway, what do you say I let you practice on Bunny a few times, and then we can find you your own broodfilly?"

Antiderivative beamed and ran to his father, wrapping him in a big hug. "Thank you, Daddy! I can't wait! I guess I'm really a stallion now, huh?"

Dr. Diffy Q just smiled, nodded, and hugged back.