3.6.3 Convert to Function
An equation is converted to a function by using the single variable
on either side as the name of the function and inferring arguments
from variables on the other side. If both sides are variables,
the left side is used as the name of the function.
If neither side is a variable and one side is 0,
a unique name is generated and arguments are inferred from the other side.
Thus
The elaboration of the function is whichever expression was used to infer the arguments.