Description: Lemma for cvmlift . In cvmliftlem15 , we picked an N large
enough so that the sections ( G " [ ( k - 1 ) / N , k / N ] )
are all contained in an even covering, and the function T
enumerates these even coverings. So 1st( TM ) is a
neighborhood of ( G " [ ( M - 1 ) / N , M / N ] ) , and
2nd( TM ) is an even covering of 1st( TM ) ,
which is to say a disjoint union of open sets in C whose image
is 1st( TM ) . (Contributed by Mario Carneiro, 14-Feb-2015)