[Tex/LaTex] non-kludgey left subscripts


I was taught to make a left subscript as a right subscript to {}. For example, I would use

f: {}_RA \rightarrow {}_RB

to typeset this:

If you instead use

f: _RA \rightarrow _RB

the left subscripts end up in the wrong place (because LaTeX thinks they are right subscripts of the object before):

However, this trick doesn't work well with operators like /otimes. The code

A {}_\varphi\otimes_\psi B

puts too much spaace between the tensor product symbol and the subscript:

One solution I've found is to use spaces (including a negative thin space) to adjust the spacing. The code

A \; {}_\varphi \! \otimes_\psi B

produces this:

However, this is a kludge and doesn't communicate to LaTeX that \varphi should be attached to the \otimes. Also, the left subscript is still just a tad too far to the left. Does anyone know a more elegant solution to this?

Best Answer

Try the tensor package. You can just issue

$A \tensor[_\varphi]{\otimes}{_\psi} B$

to get what you specified as an example. Note that if you have mixed upper and lower indices, the standard \tensor command will leave "phantom" spaces. To make all indices flush against the central symbol, use \tensor*.

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