What is the first step of the following indirect proof?

Given: The side lengths of a triangle are 4, 4, 6 Prove: The triangle is not a triangle.

The condition for that is

Let a b c be triangle sides they must verify the identities

a + b greater than c

C + a greater than b

B+c greater than a

Sum of two sides is greater than the third

In your case

Sides 4,4,6

4 + 4 gt 6

4 + 6 gt 4 true

4 + 6 gt 4 true

Its looks like a vaild triangle sides to me