TITLE: Infra-Pták space that is not Pták
QUESTION [6 upvotes]: From reading the literature of the 1970s heyday of locally convex spaces, it seems that it was an important open question whether there is an infra-Pták (i.e. $B_r$-complete) space that is not Pták (i.e. $B$-complete). Is this still open?

REPLY [4 votes]: Valdivia constructed counterexamples in his paper Br-Complete Spaces which are not B-Complete.