The following compiles just fine: `${a_b}_c$`. But when I try to add an accent over the 'a', as in `${\hat a_b}_c$`, I get an error message:

> 
> `? ! Double subscript.
>  l.1187 ${\hat a_b}_
>  c$`
> 
> 
> 

Is there a good reason for getting this error? and how can I fix it? or is it a bug in my tex distribution? I've tried putting in more braces, as in `${{\hat a}_b}_c$`, but this apparently does not help.