On cherche * tel que * m n = m*n
On a :
m*n ≡ sm*n 0 ≡ sn (sn (…(sn 0)..))
= n s (n s ( … (n s 0)..)) = m (n s) 0
* m n = m (n s) 0 = C m 0 (n s) = C C 0 m (n s)
= B (C C 0 m) n s = C (B (C C 0 m)) s n
= C C s (B (C C 0 m)) n = B (C C s) B (C C 0 m) n
= B (B (C C s) B) (C C 0) m n
On peut donc prendre
:
*
≡def
B (B (C C s) B) (C C 0)