A very natural question for algebraists is the Whitehead problem: is there an abelian group A which is not free but for which Ext^1(A, Z) = 0? Shelah showed that this natural problem was independent of ZFC. If you assume CH is false and Martin's axiom is true, then such a group exists. On the other hand, V=L, which implies CH, also implies such a group does not exist.

In set theories where Continuum Hypothesis is false, what are the new sets?
I am stumped so I hope I can present my question in a manner that allows me to get some support. I am creating a Lead validation rule  that in essence is 3 tiers i.e. if tier 1 is selected require that tier 2 is selected and if this value in tier 2 is selected require  tier 3 text to be completed. Here are my picklist requirements

Lead Source           Lead Source Details                       Complete Text Field

Wholesaler
                          &gt;ABC Wholesaler
                          &gt;XYZ Wholesaler
                          &gt;Other if other is selected complete   [text field]   

Personal Referral
                         nothing else here

Trade Show/Event
                         nothing else here but we need to &gt;   [text field]

TBP Event
                         nothing else here but we need to &gt;   [text field]

Website
                         nothing else here

Other
                          nothing else here but we need to &gt;   [text field]


When this was only a 2 tier picklist I used this validation rule but now I can't figure out how to rewrite for 3 tier

ISBLANK(Lead_Source_Details__c)
&amp;&amp;
(
    ISPICKVAL(LeadSource, "Distribution Partner")
    || ISPICKVAL(LeadSource, "Event/Trade Show")
    || ISPICKVAL(LeadSource, "TBP Event")
    || ISPICKVAL(LeadSource, "Other")
)
