Function VALUE-AT

Slots on this function:

The function value-at returns the value of a quantity at some point in 'time' (or whatever the independent state variable is). The 'time' argument is just a constant scalar-quantity, such as a time-quantity. If the quantity is a function-quantity, then its value-at is its function value applied to the 'time' argument. If the quantity is constant-quantity, then its value-at is the quantity itself for all 'times'.
Arity: 3


(Nth-Domain Value-At 2 Scalar-Quantity)

(Nth-Domain Value-At 1 Physical-Quantity)

(=> (Value-At ?Q ?Time ?Val)
    (= ?Val (If (Function-Quantity ?Q) (Value ?Q ?Time) ?Q)))