Add more explicit error message.
pac.print does not work in PAC/MCE equations.
pac.print does not work in PAC/MCE equations.
mentioned in commit d68b141c
·mentioned in commit d68b141c
mentioned in commit 5e0c4272
·mentioned in commit 5e0c4272
mentioned in commit 01d6a1c7
·mentioned in commit 01d6a1c7