Hello,

the task is to prove following theorem in propositional logic's axiomatic system (http://ww2.cs.mu.oz.au/255/lec/subject-prop_axiom.pdf):

Some basic assumptions:

For propositions A, B and C following are axioms:

The only inference rule is Modus Ponens:

I tried to use the axioms in many ways, but somehow I couldn't get the right combination. At first, the problem seems quite mechanical, but atleast I didn't know how to achieve the goal. Any help is appreciated. Thanks very much!