You are Alice and you want to send a coded message to Bob. The way you will send the message is with up and down arrows or diagonal arrows, shown below.
The way you can generate a message is with zeros and ones. When zeros and ones are passed though these + and X, arrows are generated. The only way the message can be measured is with + and X.
The compatibility of + and X with arrows is such that plus aligns the arrows along its direction and crosses align the arrows along itself, for example as shown in the figure.
If someone intercepts these messages in between and sends them to Bob, the situation will change and number of matchings will differ between Alice and Bob. The question is – How many such arrows need to be send in order for probability of matching exceeding 0.99999 even if someone intercepts in between.
