Instructions
Exercises 10: A. 3, 4. B. 2, 6, 10, 13, 18. D. 4, 13.
NB1: Please follow the instructions in each question about which logical theorems you may use and which you may not. If this is not specified, you may use any logical theorem from the list in Section 10.6 in your answer (see also NB2 next).
NB2: If there is a biconditional on the list in Section 10.6, then you may use the fact that each direction of the biconditional (as a conditional) is also a logical theorem (but be careful – not all the formulae on the list in Section 10.6 are biconditionals!).
NB3: As always, if your answer is a formal proof, then it should be fully annotated, and if your answer involves a structure, then you should explain why it does whatever it is supposed to do (in terms of making (the) relevant formula(e) true/false).