install some more reasonable methods for these mixed cases

    i2 : (new Tally from {a => 1}) + (new VirtualTally from {a => -2})

    o2 = HashTable{a => -1}

    o2 : HashTable

    i3 : (new VirtualTally from {a => 1}) + (new Tally from {a => -2})

    o3 = HashTable{a => -1}

    o3 : HashTable

reverse this relationship, since a tally should be a type of virtual tally:

    i4 : parent VirtualTally

    o4 = Tally

    o4 : Type
