[185, 96, 632]
unapply is the inverse of apply. If you apply the function named cos to Pi/2 you get cos(Pi/2), which happens to be 0.
Likewise, if you apply the function cos to x you get cos(x).
So unapply(cos(x),x) gives you the cos function. unapply takes an expression, say in the variable x, and turns it into a function.
Lots of times people confuse f(x) with f. The first is an low-life "expression" while the second is a more dignified, abstract thing called a function.
Note that t^2 and x^2 are different expressions, but
unapply(t^2,t) and unapply(x^2,x) are equal functions.
You might enjoy a Google search using key words
Church lambda calculus.
Alonzo Church developed something called the lambda calculus. He would write something like
Or lambda x(x^2) is the same as the Maple proc
Church's lambda abstraction operator is the same as Maple's unapply.
It would also be nice if Maple could tell us how long it will take to solve the Riemann hypothesis.
Or if a Turing machine will halt.