If[Condition, Object]: Yields a copy of the object if the condition evaluates to true, and an undefined object if it evaluates to false.
If[Condition, Object a, Object b]: Yields a copy of object a if the condition evaluates to true, and a copy of object b if it evaluates to false.
IsDefined[Object]: Returns true or false depending on whether the object is defined or not.
IsInteger[Number]: Returns true or false depending whether the number is an integer or not.