Use deductive reasoning to tell whether each statement is true or false. If it is false, give a counterexample.
22. For all real numbers a and b, a - b = -b + a.
23. For all real numbers p, q and r, p - 4-r=p-r-q.
24. For all real numbers x, y and z, (x + y) + z = z + (x + y).
25. For all real numbers m and n, m. n = n. m.​