First of all let me write what I understand from your post: Because there're no Sections in the IPC on Instigation and Provocation you feel that these are not offences.
Madam. There's no Section on Kicks. Is kicking not an offence? Can you go on kicking others?
But I hate the above amteurish reasoning.
My New Oxford Dictionary of English ( NODE ) says:
instigate someone to/to do something incite someone to do something, especially something bad.
You told you'd instigated. Something good? Nevertheless he slapped? One doesn't incite a person to stop bad habits. One advises, encourages.
The above reasoning too is amateurish.
provocative: causing annoyance, anger, or another strong reaction especially deliberately
You caused anger in him and he slapped.
provoke: stimulate or give rise to ( a reaction or emotion, typically a strong or unwelcome one ) in someone.
Now let me draw your attention to Section 504 of the IPC. Didn't you insult him? You did. Hence he slapped. And he committed another offence. So Sec 504 is attracted and you committed an offence.
Now to Defamation. You said something. He felt himself defamed. Hence he slapped. Now your contention would be whatever you said was true. May be. But you can't say so. A man may say, " Bastard!" It's not defamation. A man can't say, " Your mother slept with him." The man may be true. But he should not say so. It's defamation.
If you say advocates are dishonest, it's not defamatory. If you say those advocates are dishonest, it's defamatory.
'Avocates are Kajia-Dalals' is not defamatory unless it aims at a particular group of advocates. Narottamdas L ShahMaganbhai Revabhai 1984 Cr L J 1790 (Guj)
I have found a few other case laws.
Please write if you want much more elaboration.