+where the '*' means 'LoopBreaker'. Then if we float we must get
+
+ Rec { g'* = /\a. ...(g' a)... }
+ NonRec { f = /\a. ...[g' a/g]....}
+
+where g' is also marked as LoopBreaker. If not, terrible things
+can happen if we re-simplify the binding (and the Simplifier does
+sometimes simplify a term twice); see Trac #4345.
+
+It's not so simple to retain