I want to know if there is a finite set of identities that characterize the equational theory of the ordinal $\varepsilon_0$ under addition, multiplication, exponentiation, $0$, and $1$. $\varepsilon_0$ is understood to be the set of ordinals less than $\varepsilon_0$. I conjecture that these identities are sufficient:
- $x+0=x$
- $0+x=x$
- $(x+y)+z=x+(y+z)$
- $x*0=0$
- $0*x=0$
- $x*1=x$
- $1*x=x$
- $(x*y)*z=x*(y*z)$
- $x*(y+z)=(x*y)+(x*z)$
- $x^0=1$
- $x^1=x$
- $1^x=1$
- $x^y*x^z=x^{y+z}$
- $(x^y)^z=x^{y*z}$
Are these sufficient, or do we need a few more identities? Or is it not in fact finitely axiomatizable?