Find the results of the following substitutions. Just give the answer and explain the reasons if the result is undefined:
a) (∀𝑥)(𝑓(𝑥) < 7)[𝑥 ≔ 7]
b) (∀𝑦)(𝑓(𝑥) < 7)[𝑥 ≔ 7]
There is nothing to substitute x to on both questions and will be therefore undefined?