Lets continue with the 4 brothers we met last time: A(rthur), B(ernard), C(harles), D(avid). Where A is an accurate truth-teller, B is an inaccurate truth-teller (all is beliefs are incorrect, but he never lies about it), C is an accurate liar and D is an inaccurate liar (he's both delusional and dishonest).
Q6: https://www.facebook.com/groups/mockamockingbird/permalink/157621477958293/

This is a preparation for the next puzzle:
Lets discuss a basic principal about accurate and inaccurate truth-tellers and liars. If you ask the 4 brothers whether 2+2=4, A & D will say Yes, and B & C will answer No.
What if I ask "Do you believe that 2+2 equals 4?"
What will each brother answer?