Alas, mutable Set/Bag/Mix follow different rules
Alas, mutable Set/Bag/Mix follow different rules

This reverts commit 22d8cd42ba02f242489a466d8e2377974cbb1cb5.

perl6/specs,prammer/specs,tokuhirom/specs,perl6/specs,tokuhirom/specs,tokuhirom/specs,prammer/specs,prammer/specs