Indeed, it is a fiction to talk of separation of powers in a presidential system as the three branches of government interact with one another in diverse ways in order to ensure the smooth operation of government.
Such instances of cooperation or balancing acts are ironically examples of checks and balances.
The difference between the two figures is very simple. Theft consists of the stealing of someone else's property without using violence, force or intimidation while robbery consists of appropriating the property of others using force (forcing or breaking doors, windows or any other means of access), violence (physical) or intimidation (verbal or gestural).