Important points Chapter 2 book 1

Logical statements are also called propositions

Negation is unairy operation.

Conditional is equivalent to contrapositive.

Converse is equivalent to inverse.

Tautology means ⇾always true.

Absurdity ⇾ always false.

Contingency ⇾either true or false.

MCQ:

(p⇾q) ⇾(∼q⇾∼p) is:

a)    Tautology

b)   Absurdity

c)    Contingency

d)   None of these

Don’t draw the table to check it. You are not provided much time to draw a table for this type of MCQs. First check the conditions carefully.

As conditional is equivalent to contrapositive so it is a tautology. (a)

Residue classes:

In residue class 4:

1)   0 is identity.

2)   3 is the inverse of 1.

3)   2 is the inverse of 2.

4)   1 is the inverse of 3.

Same is in the case of other residue classes depending upon the class.