In text-based interfaces it is very common today [*] to see auto-completion for reason of performance and to help remember syntax and avoid having to look up keywords as well.

[*] (IDEs, shells like zsh or bash, ...)

Hence it would be nice to see possibilities that start with what I typed for all the (command) "keywords" that soulver knows:

e.g. 5.5 as t

should result in "timespan" appearing (should be visually different than if I already had typed timespan, e.g. greyed out text) and you can confirm this proposition via TAB.

or if there are multiple possibilities then they should be listed and you can enter this list with tab/shift-tab and to choose you hit ENTER in this case

(or alternatively cursor-up /-down and to chose you hit ENTER or TAB)

IMHO the cursor-key selection is unelegant as it means lifting the hand off the keyboard to the cursor-keys, whereas the TAB key can easily be entered leaving both hands on the keyboard.