A proof of a claim is given below.

Claim. There is no largest natural number.

Proof. Suppose such a natural number n exists.

Then for any natural number m, m < n. Now let m = n + 1. Then n + 1 < n. This is a contradiction. Thus .... Determine which of the following is false.

(a) This is a proof by contradiction.

(b) The proof is valid.

(c) This is a proof by contraposition.

(d) none of these