gioco matematico: due cerchi

Material: two strings

Procedure:
bind each ends of the two strings so as they can pass through the hands of the boys. It must be a bit wide.
give one end of the first string to the first boy.
the boy passes the bound string through his right hand.
cross the second string.
give one end of the second string to the second boy.
the second boy passes one end of the second string through his own left hand.
the first boy passes the other end of the first string through his own left hand.
the second boy passes the other end of the second string through his own right hand.
now the two boys must be tied and the two strings should be crossed. It is like two circles crossing one into the other.

The two boys have to get  loosed.

Enjoy!!!!!!!