1. s : DSet
2. a : |s|
3. b : |s|
⊢ uiff(↑(a (=b) b);a = b ∈ |s|)
{ AddProperties 1
THEN UnfoldTopAb 2
}
2. ∀[x,y:|s|]. uiff(↑(x (=b) y);x = y ∈ |s|)
3. a : |s|
4. b : |s|