This reverts commit 849abb8d, reversing changes
made to 8de0b894.  The merge was done
accidentally, before review happened.

This way, it can be used with `iApply`.

This is to be used on top of stdpp's 4b5d254e.

Use COFEs only for the recursive domain equation solver

This fact is deduced from reducibility. Unfortunately, this sometimes depends on the type of states being inhabited, so that this additional hypothesis sometimes appear.