Asimov

First Law:
A robot may not injure a human being, or, through inaction, allow a human  being to come to harm.

Second Law:
A robot must obey orders given it by human beings, except where such orders would conflict with the First Law.

Third Law:
A robot must protect its own existence as long as such protection does not  conflict with the First or Second Law.

Fourth Law: (where did this arrive from)
A robot must perform the duties for which it has been created.

The Meta-Law:
A robot may not act unless its actions are subject to the Laws of Robotics

The Zeroth Law:
A robot may not injure humanity, or, through inaction, allow humanity to come to harm.

A summary of the Asimov Laws would give us the following 'truth table'.
1. A robot must obey human orders with the following two exceptions:
a) That obeying them will cause injury to a human through an action or
b) That obeying them will let a human be injured.

2. A robot must protect its own existence with three exceptions:
a) That such protection will be injurious to a human
b) That such protection entails inaction in the face of potential injury to a human
c) That such protection will bring about robot insubordination
   [not obeying human instructions].