I have to functions a(F) and |F| where F is a propositional formula The first one return the number of all propositional variables and the second one returns the number of all propositional variables, brackets and connectors
ex: a( (not b) ) = 1 |(not b)| = 4
I have to use structural induction to prove that for any formula F a(F) <= |F|
I don't really understand structural induction and I have no idea how to solve this.