There are two commands, send, and reply, for a simple electronic mailing system. Assuming

that each message has a unique name, give specifications in extended BNF for

these commands. The requirements are:

$$ A message can be sent by a user to one or more users in the system.

$$ A user can reply to only one mail at a time. The effect of reply is to compose a

message, assign a unique name, assign a time$-$stamp, and send the message to the

user from whom the original message was received.