If $tau_1$, ..., $tau_n$ are numerical constants, then the term {tt (+ $tau_1 ... tau_n$)} denotes the sum $tau$ of the numbers
corresponding to those constants.
and also:
Q+ is the nary q-operator for adding several q-expressions.Eg: (Q+ (Term-12 current) (Term-13 current) (Term-14 current)).
(Undefined (Arity +)) (Undefined (Arity +)) (Undefined (Arity +)) (Undefined (Arity +))