组合的定义

ab和ba是同一种组合

The issue states that 'ab' and 'ba' should be considered the same combination, but does not specify where in the code this logic is implemented or failing. Look for functions handling combinations or permutations in the Nim source files. Check if there are existing tests for combination calculations to understand the expected behavior. The goal is to ensure the program treats 'ab' and 'ba' as identical in combination outputs.

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