1650, 52-year-old Descartes met 18-year-old Swedish princess Christine on the streets of Stockholm. Descartes, who was down and out at that time, lived a life of begging, and all his possessions were only his tattered clothes and a few math books with him. Descartes, with a lofty nature, never asked passers-by for alms. He just silently bowed his head and wrote on the paper, immersed in his mathematical world. On a quiet afternoon, Descartes sat in the street as usual, bathed in sunshine and studied math problems. He is so addicted to the world of mathematics, to the people passing by, and to the noisy cars and horses. You can't interfere with him. Suddenly, someone came up to him and patted him on the shoulder. "What are you doing?" Turning around, Descartes saw a beautiful young eyelid, a pair of clear eyes like a blue lake, lovely long eyelashes blinking, waiting for his response. She is the little princess of Sweden and the king's favorite daughter Christine. She bent down, took Descartes' math book and draft paper, and began to talk to him. During the conversation, he found that the little girl was quick-thinking and interested in mathematics. After saying goodbye to the girl, Descartes gradually forgot about it and still sat in the street every day to write and draw. A few days later, he was unexpectedly informed that the king hired him as the little princess's math teacher. Descartes was full of doubts and came to the palace with the guards who came to inform him. While waiting in the living room, he heard a silvery laughter coming from a distance. Turning around, he saw the girl he met in the street the day before yesterday. In desperation, he bowed his head and saluted. From then on, he became the princess's math teacher. Under the careful guidance of Descartes, the princess's mathematics advanced by leaps and bounds, and they began to become close. Descartes introduced her to his new research field-rectangular coordinate system. Through it, algebra and geometry can be combined, which is the embryonic form of analytic geometry founded by Descartes later. Under the guidance of Descartes, Christine entered the wonderful coordinate world, and she was fascinated by curves. Being inseparable every day also makes them fall in love. In this romantic country of Sweden, a pure and beautiful love has quietly sprouted. However, it didn't take long for their love affair to reach the king's ears. The king was furious and ordered Descartes to be executed immediately. At Christine's pleading, the king exiled him to China, and the princess was placed under house arrest. At that time, the Black Death was prevalent in continental Europe. Descartes, who was weak, fell ill soon after he returned to France. In the countdown to life, what he misses day and night is the warm smiling face he met in the street. He writes to her every day, expecting her reply. However, these letters were intercepted by the king and the princess never heard from him again. Descartes sent Christine his thirteenth letter and died forever. At this time, the little princess under house arrest is still wandering in the corridor of the palace, thinking of her lover in the distance. There is not a word written in this last letter, but only one equation: r=a( 1-sinθ). The king couldn't understand it, thinking that there were two secrets hidden in this equation, he called all the mathematicians in the city to his palace, but no one could work out this function. He couldn't bear to see his beloved daughter moping every day, so he gave her this letter. Christine was ecstatic when she received the letter. She immediately understood her lover's intention, found paper and pen, and began to draw equation diagrams. A heart-shaped pattern appeared in front of her eyes, and Christine couldn't help crying. This curve is the famous "heart line". After the king died, Christina succeeded to the throne. Immediately after she ascended the throne, she sent someone to France to find the whereabouts of her sweetheart. What she received was the news of Descartes' death, which left an eternal regret ... This world-famous alternative love letter is still preserved in the Descartes Memorial Hall in Europe.

The concept of replacement in the advertisement is to compare the water in Baisui Mountain to this kind of alternative love letter, which means that the story of "classic romance is unforgettable" is good, the concept is good, and the creation is good, but the advertisement is bright and blind.