# Automatic subscript command

I am working on a document that has a lot of subscripts. I am getting really tired typing the _. Is there a way to do the following:

Everytime I want $v_1$, I just want to type in v1. Or b1 produces b_1 or c1 produces c_1.

Bonus points for someone who can teach me how to do something like b{1 and 2} for b_{1 and 2} or something even more robust where I can specify whether its a superscript or a subscript.

I understand this might end up in more keystrokes but I'd rather have simple keystrokes than moving my hand across the keyboard for the underscore.

I also realized I don't use the number pad. Is there a way to hotkey the number pad so that press "1" on the number pad will insert \textbf{} for me or something similar -- this might be posted as another question

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see recent questions for reasons why it's a bad idea to do this, and possible solutions if you wish to do it anyway Expanding subscript and subscript capabilities and alternative syntax of subscripts using tex –  David Carlisle Jan 31 '13 at 22:54
Regarding your question about "hotkeys", this is a feature of your editor, not of TeX/LaTeX, and as such it is off-topic on this site. Regarding your main question, I am not sure what you want: is it that any digit following a letter should be subscripted? –  Bruno Le Floch Jan 31 '13 at 22:55
@BrunoLeFloch Yes. Any series of numbers should be subscripted. b2343 means b_2343 –  masfenix Jan 31 '13 at 23:39
If zou might the difficultz of tzping _ then zou could trz a different kezboard lazout. The German lazout has the _ kez just left the shift kez, making it easilz accessible. But, there are drawbacks: the y and z kez are exchanged for example... –  Martin Scharrer Jan 31 '13 at 23:39
I see. I believe you might be using a different layout where your z is switched with y :) –  masfenix Jan 31 '13 at 23:41

This is implemented in mhchem package: \ce{H20} produces an equivalent to $\mathrm{H}_2\mathrm{O}$. You may want to either use this package directly or look into its code to borrow ideas.
I think the OP asks for a way without the \ce{} macro letting TeX parse the scripts. –  percusse Jan 31 '13 at 23:29
Chemical formulas are very specialized and one can assume that every number (after a letter) in them is a subscript; what about $b1+1$? And b23 should mean b_{2}^{3}, b_{23}, b^{23} or b^{2}_{3}? –  egreg Jan 31 '13 at 23:34
Well, Martin Hensel put some nice heuristics in the package: \ce{b1+c} means $b_1^+ c$, while \ce{b1 + c} means $b_1 + c$, \ce{b23} means $b_{23}$ etc. You always can use explicit _ and ^ with grouping to override, but defaults work fine in 90% of cases and turn out to be very useful when you quickly type, e.g. making notes during a talk. I agree that outside of chemistry a different set of defaults should be designed. –  Boris Jan 31 '13 at 23:40