Postulates and Theorems of Boolean Algebra
Postulate 2 x+0 = x x⋅1 = x
Postulate 5 x+x′ = 1 x⋅x′ = 0
Theorem 1 x+x = x x⋅x = x
Theorem 2 x+1 = 1 x⋅0 = 0
Theorem 3,
Involution
(x′)′ = x
Postulate 3,
commutative
x+y = y+x xy = yx
Theorem 4,
associative
x+(y+z) = (x+y)+z x(yz) = (xy)z
Postulate 4,
distributive
x(y+z) = xy+xz x+yz = (x+y) (x+z)
Theorem 5,
DeMorgan
(x+y)′ = x′y′ (xy)′ = x′+y′
Theorem 6,
absorption
x+xy = x x(x+y) = x
Important Proof

1. A + AB = A

2. A . (A + B) = A

3. A + A'B = A + B

4. A . (A' + B) = AB

5. AB + BC + A'C = AB + A'C

6. (A + B) (B + C) (A' + C) = (A + B) (A' + C)

Duality

To find duality convert (+) to (.) or vice-versa

Example: A + B = A . B

Complement of a Function

Step 1: Find the dual of the function.

Step 2: Complement each literals/varaibles.

Example: F1 = X'YZ' + X'Y'Z

S1 => F1 = (X' + Y + Z') . (X' + Y' + Z)

S2 => F1' = (X + Y' + Z) . (X + Y + Z') //answer

Canonical and Standard Forms
Sum of minterms

A minterm, denoted as mi, is a product (AND)
uncomplemented X = 1,
complemented X' = 0

Example :
F = x + yz
= x (y + y') (z + z') + (x + x') yz
= xyz + xyz' + xy' z + xy' z' + xyz + x' yz
= x' yz + xy' z' + xy' z + xyz' + xyz
= m3 + m4 + m5 + m6 + m7
= ∑(3, 4, 5, 6, 7)

Product of maxterms

A maxterm, denoted as Mi, is a product (OR)
uncomplemented X = 0,
complemented X' = 1

Example :
F = (x+y+z) • (x+y+z') • (x+y'+z) • (x'+y+z)
M0•M1•M2•M4
= ∏(0, 1, 2, 4)


x y z Minterms Maxterms F F'
0 0 0 m0= x'y'z' M0= x+y+z 0 1
0 0 1 m1= x'y'z M1= x+y+z' 1 0
0 1 0 m2= x'yz' M2= x+y'+z 0 1
0 1 1 m3= x'yz M3= x+y'+z' 1 0
1 0 0 m4= xy'z' M4= x'+y+z 1 0
1 0 1 m5= xy'z M5= x'+y+z' 0 1
1 1 0 m6= xyz' M6= x'+y'+z 0 1
1 1 1 m7= xyz M7= x'+y'+z' 0 1

Canonical form and Standard Form
  • Canonical form -
    • Sum of minterms (SOM)
    • Product of maxterms (POM)
  • Standard forms (may use less gates) -
    • Sum of products (SOP)
    • Product of sums (POS)
  • SOP form may not be in Canonical Form
  • F = ab+a’ (already sum of products:SOP)
    F = ab + a’(b+b’) (expanding term)
    F = ab + a’b + a’b’ (it is canonical form:SOM)