1 x instanceof f: true

     2 x instanceof b: true

     3 y instanceof f: true

     4 y instanceof b: true

     5 

     6 Changing prototype

     7 

     8 x instanceof f: false

     9 x instanceof b: false

    10 y instanceof f: false

    11 y instanceof b: false

    12 Bound function prototype

    13 

    14 f.hasOwnProperty('prototype'): true

    15 b.hasOwnProperty('prototype'): false