If $tau$ and $tau_1$, ..., $tau_n$ denote numbers, then the term {tt (- $tau$ $tau_1 ... tau_n$)} denotes the difference between the
number denoted by $tau$ and the numbers denoted by $tau_1$ through $tau_n$. An exception occurs when $n=0$, in which case the term denotes the negation of the number denoted by $tau$.
and also:
Q- is (i) the unary q-operator for expressing the negation of aq-expression (ii) the binary q-operator for expressing the difference between its 2
q-expression arguments.
Eg: (Q- (Term-14 voltage)) (Q- (Term-12 current) (Term-13 current))
(Undefined (Arity -)) (Undefined (Arity -)) (Undefined (Arity -)) (Undefined (Arity -))