The question is to simplify this λ-expression (λx. x) (λx. λy. y x) 8 (λx. x + 1)
My current thinking is as follows (λx. x) (λx. λy. y x) 8 (λx. x + 1) = (λx. λy. y x) 8 (λx. x + 1)
(λx. λy. y x) 8 (λx. x + 1) = (λy. y 8)(λx. x + 1)
(λy. y 8)(λx. x + 1) = (λx. x + 1)(8)
(λx. x + 1)(8) = 8+1 = 9
However, I am told the answer is 72. why would the 9 multiply the previous 8 after it's substituted in?