The best replacement for proofs is uncirculated coins.

The best alternatives to proofs are rated as following:
★★★★★  uncirculated coins
★★★★  prints
★★★  proves
★★★  proof
★  signed prints

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Speaking about proofs, one probably shouldn't forget about coordinate geometry.

Other search terms related to proofs and their ratings are:
★★★★★ coordinate geometry
★★★ prime numbers
★★ quantifiers
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proofs
uncirculated coins
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