(1) All three X's are constrained variables, and Y is free variables, which is the first one? The range of x is the first P(x) and the second p (x)? The range of x is the second P(x). The range of x is Q(x).

(2) X, Y and Z are all constrained variables.

(3)x, Y are constrained variables, and Z is free variables.

(4) X in A (x) is a constraint variable, X in B(x, y) is a free variables, and Y is a constraint variable.

(5) x in f (x) is a constraint variable, y in G(x, y, z) is a constraint variable, x and z are free variables, z in H(x, y, z) is a constraint variable, and x and y are free variables.

Discrete mathematics is a mathematical discipline that studies the structure and relationship of discrete quantities and an important branch of modern mathematics. Discrete means that different elements are connected together.