# Grouping substitution rules makes the kernel unresponsive

Hello,

First of all thank you for this wonderful software! I have been using it for a few months now to compute analytically some expressions in nuclear physics, and I recently upgraded to the Dec10 version as collect_factors could finally act on objects with symbol indices.

However, the same code I have been using with an older version (Nov17) does not work any more. I narrowed it down to the grouping of a number of substitution rules together. As an example,

rules:={a->b, a->b, ..., a->b};


for a large enough number of rules (between 128 and 256) makes the kernel unresponsive.

For the actual code I have been using, the number is smaller as the rules are more complicated. Also, if started from the terminal, it shows the output:

recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **
recursive end **

If it helps, I am using Cadabra on Ubuntu 18.04. Also, please let me know if you need my actual code for further clarification.

Thank you very much!