When we have a sentence of the form: What + sb + verb + [be (in the appropriate tense)] + ... (for instance, what I like is ...), which rules do we have to apply to determine whether the sentence is followed by to + infinitive or a gerund? Are these rules the same ones that we use when deciding if the verb is followed by to + infinitive or a gerund?
(what-cleft or pseudo-cleft)
This one is used to emphasize.
I liked to have a talk with her on the phone.
What I liked was (to) have a talk with her on the phone.
If you want to emphasize the verb "have", you can omit "to".
You can use to-infinitive or infinitive itself.
This is just a some high level grammar.