This comes from the discussions on this PR https://github.com/sympy/sympy/pull/7462#issuecomment-42111992
We have a class called UniversalSet which is supposed to be *set* which contains all the sets which we can define in Sympy. The problem is that we really don't "know" what our defined Universal Set is. It has been proposed by Sergey that we wipe out the Universal Set class. We can explicitly provide the the known defined universal set when situation asks for it, that set can be complex, real or real*real or anything. I'm +1 to the proposal. I guess this goes with "Explicit is better than Implicit" from the Zen of Python. At places we are implicitly assuming UniversalSet to Interval(-oo, oo) which is clearly wrong. Then we cannot define operations like PowerSet and cardinality on such sets. We can avoid the problem by leaving PowerSet or cardinality undefined for UniversalSet, but not having an UniversalSet will be a better way to avoid unknown inconsistencies. I want to know the views of the community on this matter. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/189a8ed3-cea8-49be-a1d6-1b650bea4c3c%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
