数学符号的弹出式纸艺工程

一本打开的书上，四个大型数学符号以弹起式纸艺工程的形式呈现，构成一个 2x2 的网格。
[左上：积分符号 (∫) 呈现为高耸的纸质拱门，分层纸艺，印有微型文字的方程式作为壁纸]
[右上：求和符号 (Σ) 呈现为折叠纸质博物馆，带有锐利的折纸悬臂、光影效果和图表标注]
[左下：圆周率符号 (π) 呈现为分层卡纸制成的弹起式古典大门，带有风化的墨迹纹理和微小的纸质行人]
[右下：克莱因瓶的轮廓呈现为不可能的弹起式雕塑，可见纸质标签和连接线，优雅的悖论几何]
桌面编辑照明，浅景深，清晰的纸张纤维，书籍装帧细节，墨迹图表，瑞士网格布局，超干净的微缩写实主义。

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**Original English:**
A 2x2 grid of 4 large mathematical symbols built as pop-up paper engineering on an opened book
[Top Left: The Integral (∫) as a towering paper archway, cut-paper strata, printed equations as microtext wallpaper]
[Top Right: The Sigma (Σ) as a folded paper museum with sharp origami cantilevers, shadow play, diagram callouts]
[Bottom Left: The Pi (π) as a pop-up classical gate in layered cardstock, weathered ink textures, tiny paper pedestrians]
[Bottom Right: The Klein bottle silhouette as an impossible pop-up sculpture, paper tabs and join lines visible, elegant paradox geometry]
Tabletop editorial lighting, shallow DOF, crisp paper fibers, bookbinding details, inked diagrams, swiss grid layout, hyper-clean miniature realism.