I'm coming back to one of my previews ticket (https://toolset.com/forums/topic/conditional-output-based-on-cart-input/).
Nigel explained (You'll need to write a custom function to check if a product is in the cart, and you can then use the results of that function in your condition).
I would like to know what should be the result of this function to be used inside a Toolset conditional. Should it be a true / false result or something else? When used in a conditional in general, what is the expression that the condition is waiting for (in order to built the function returning exactly this expression).