## Last version: 8 July 2019

class Multiset:
    
    ## Multiset() produces a newly constructed empty multiset.
    ## __init__:  -> Multiset
    def __init__(self):

    ## value in self produces True if value is an item in self.
    ## __contains__: Multiset Any -> Bool
    def __contains__(self, value):

    ## self.add(value) adds value to self.
    ## Effects: Mutates self by adding value to self.
    ## add: Multiset Any -> None
    def add(self, value):
    
    ## self.delete(value) removes an item with value from self.
    ## Effects: Mutates self by removing an item with value from self.
    ## delete: Multiset Any -> None
    ## Requires: self contains an item with value value
    def delete(self, value):