Interrupt[] generates an interrupt.
KroneckerDelta[n_1, n_2, ...] gives the Kronecker delta \[Delta] Subscript[n, 1] Subscript[n, 2] ..., equal to 1 if all the n_i are equal, and 0 otherwise.
Locked
(Built-in Mathematica Symbol) Locked is an attribute that, once assigned, prevents modification of any attributes of a symbol.
Modal
(Built-in Mathematica Symbol) Modal is an option to functions such as CreateDialog that specifies whether the dialog that is created should be modal to the Mathematica front end.
NameQ
(Built-in Mathematica Symbol) NameQ["string"] yields True if there are any symbols whose names match the string pattern given, and yields False otherwise.
NumberQ
(Built-in Mathematica Symbol) NumberQ[expr] gives True if expr is a number, and False otherwise.
PageBreakWithin is an option for Cell which specifies whether a page break should be allowed within the cell if the notebook that contains the cell is printed.
PossibleZeroQ[expr] gives True if basic symbolic and numerical methods suggest that expr has value zero, and gives False otherwise.
PowerModList[a, s/r, m] gives a list of all x modulo m for which x^r \[Congruent] a^s mod m.
PreferencesPath is a global option that specifies which directories are searched for user-specific settings when Mathematica is started.