Chordal Graphs

One can prove the following propositions: (1) For every non zero natural number n holds n − 1 is a natural number and 1 ≤ n. (2) For every odd natural number n holds n − 1 is a natural number and 1 ≤ n. (3) For all odd integers n, m such that n < m holds n ≤ m − 2. (4) For all odd integers n, m such that m < n holds m + 2 ≤ n. (5) For every odd natural number n such that 1 6= n there exists an odd natural number m such that m + 2 = n. (6) For every odd natural number n such that n ≤ 2 holds n = 1. (7) For every odd natural number n such that n ≤ 4 holds n = 1 or n = 3. (8) For every odd natural number n such that n ≤ 6 holds n = 1 or n = 3 or n = 5. This work has been partially supported by the NSERC grant OGP 9207.