Choose the correct alternatives (more than one may be correct) and write the corresponding letters only:
Which of the following is/are a tautology?
How to treat option D? (the associtivity) a->(b->(b->c)) or (a->b)->(b->c)
-> is right associative according to 2nd ans by http://math.stackexchange.com/questions/12223/associativity-of-logical-connectives