In this talk, I will construct certain rational functions on the moduli stack of Drinfeld shtukas, and use them to generate linear relations between the classes of horospherical divisors to give an explicit version of Manin-Drinfeld theorem for shtukas. The rational functions are somewhat similar to modular units on elliptic modular curves. If time permits, I will introduce the notion of toy shtukas, which is helpful in the study of those rational functions.

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