63) How many boolean functions of three variables f(x, y, z) have the property that f(x, y, z) = (f(x, y, z)) ?

64) A graphical display of the fundamental products in a truth-table is known as

65) Consider following switching function:
f(w, x, y, z) = w'x' + w'x y'+ wx'z'+ wxy
For this function, which of the following is list of essential prime impicants ?

66) If set x = {a, b, c, d}, then number of binary operations that can be defined on x is

67) The number of Boolean functions that can be deined for n Boolean variables over k-valued Boolean algebra are