2.1, due on 1/10

1. I thought it was strange how the notation [a] could be an infinite number of different sets, depending on the congruence modulo number.  It seems like a subscript could have been added outside of the bracket to indicate the congruence modulo number.  The introduction of the sets of all congruence classes modulo n was not very clear and it was unclear the utility of them.

2. I thought it was interesting how two congruence classes could only be disjoint or identical.  This is slightly counterintuitive but the proof was very straight forward.  I am pretty sure I have seen congruence classes before but it is still unclear to me the usefulness of them.