This is a revised version of problem posted here named :Does $p(a) = p(b) \Rightarrow a=b \ $?
Let $S=(P_1,P_2,…,P_n)$ be a set of polynomials with complex coefficients.
I call S critical if it satisfies 2 conditions.
1.set of solutions of ($P_n(a)=P_n(b)\ \ |\forall n$) in $\Bbb C^2$ is (a=b) and
2.(ADDITIONAL CONDITION)(The subfield $K =\Bbb C(P_1(z),P_2(z) ,..,P_n(z))$ of $\Bbb C(z)$ does not contain z(i.e. K is a proper subfield))
I call a set minimal critical set if it is a critical set but no proper subset of it is critical.
Does There exist a minimal critical set?
if yes does there exist minimal critical sets of cardinality n for every n ?
What if we weaken condition ($a=b$) to {($a=b$) U (some finite points in $\Bbb C^2$)}? what about above questions? ((I think the set $(Z^2+Z,Z^4)$ works here but i am not sure , i dont know whether $\Bbb C(Z^2+Z, Z^4)= \Bbb C(Z)$or not) ),