Monday, 6 June 2011

ac.commutative algebra - What is the transcendence degree of Q_p and C over Q?

In both cases the transcendence degree is the cardinality of the continuum. CH is not needed.



This is a corollary of the following result: let K be any infinite field, and let L/K be any extension. Then



# L = operatorname{max} (# K, operatorname{trdeg}_K L).



To prove this, in turn it suffices to establish the following two results (each of which is straightforward):



1) If K is infinite and L/K is algebraic, then # L = # K.



2) If K is any infinite field, T=tiiinI is an arbitrary set of indeterminates and K(T) is a purely transcendental function field in the indeterminates T, then # K(T) leq # T + # K.

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