How to have a comma most distinct from a prime

Question

At times, students in some introductory classes mistake the comma after an equation for a prime. This occurs for example if the comma shows up after a fraction, in which case the student thinks it is a prime on the denominator of that fraction.

The display and MWE in this example shows comma vs prime and it appears that using the Palatino font makes the issue worse, as in comparison with the Euler font. There, the remedy that is sought is to raise the location of comma after a fraction.

My question is in what font will comma look most distinct from a prime? For example a comma looking like a semi circle might be better for such situations.

A modified version of above MWE is reproduced below.

\documentclass{minimal}
\usepackage{amsmath}
% To use Palatino
\usepackage{mathpazo}

% To use  Euler
%\usepackage[small, euler-digits]{eulervm}
\begin{document}
 Question: which font accentuates the difference between prime and comma most?
Example 1. Comma after fraction vs prime on  denominator
\begin{equation}
 a = \frac{1}{A+B}, \qquad b = \frac{1}{A+B'}
 \end{equation}
Example 2 : prime on left side of case with comma after the case
\begin{equation}
 \left{\begin{matrix}
 x'&= 3x-2y \
 y'&= 2x-2y \end{matrix}\right. , 
 \end{equation}
\end{document}