# Why doesn’t AMPL interpret the expression T..1 as I expect?

**URL:** <https://discuss.ampl.com/t/why-doesn-t-ampl-interpret-the-expression-t-1-as-i-expect/64>\
**Category:** FAQs\
**Tags:** sets-and-indexing\
**Created:** [December 15, 2021, 5:46pm UTC](https://discuss.ampl.com/t/why-doesn-t-ampl-interpret-the-expression-t-1-as-i-expect/64 "2021-12-15T17:46:12Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![megrobert](https://avatars.discourse-cdn.com/v4/letter/m/d07c76/32.png) [@megrobert](https://discuss.ampl.com/u/megrobert)\
**Post date:** [December 15, 2021, 5:46pm UTC](https://discuss.ampl.com/t/why-doesn-t-ampl-interpret-the-expression-t-1-as-i-expect/64/1 "2021-12-15T17:46:12Z")

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In general, AMPL interprets `a..b` as `{a, a+1, a+2, ..., b-1, b}` . Thus when `T` is greater than one, `T..1` is an empty set. To specify the ordered set that goes from `T` down to `1` , write `T..1 by -1` .