limits.md

Representing upper/lower limits

Below are some possibilities for different ways one might represent a number $x$ that is an upper limit or lower limit.

Upper limit	Lower limit	Commentary
$x_{-\infty}^{+0}$	$x_{-0}^{+\infty}$	Infinities are not always well-behaved
$0_{-0}^{+x}$ (if $x>0$)	$0_{-|x|}^{+0}$ (if $x<0$)	Be careful of divide-by-zero errors; makes sense only if quantity has a true limit at zero (for instance, we expect fluxes to be strictly ≥0 physically)
$x_{-x}^{+0}$ (if $x>0$)	$x_{-0}^{+|x|}$ (if $x<0$)	Poor representation of a true limit if errors are on the order of the nominal value anyway.