We've now written a Believes predicate that can be used to ask about the beliefs of a character.  When we call it, it only answers one belief of the character.  What if we wanted to know all of the character's beliefs?  We'd like some kind of predicate like [BeliefsOf ?character ?beliefs] that, given a ?character tells us (all) their beliefs.  But ?beliefs is just one argument; how can BeliefsOf communicate a whole list of items as a single parameter?

The answer is to put them in a tuple.  Each element of the tuple is a belief, but the number of elements depends on the number of beliefs the character has.  Such tuples that are used to represent lists of things are often referred to, unsurprisingly, as lists.  But a list is just a tuple.

Here's a definition for BeliefsOf.  It uses another predicate, FindAll, that we will discuss later.  For the moment just try running [BeliefsOf john ?] and [BeliefsOf richard ?]:

# Try: [BeliefsOf john ?]
[predicate]
BeliefsOf ?character ?beliefs: [FindAll ?b [Believes ?character ?b] ?beliefs]

[predicate]
Believes john god_exists.
Believes john [important money].
Believes richard god_exists.
Believes richard [important helping_people].
Believes john [Friends john richard].
Believes john [Friends john elon_musk].
Believes richard [Friends john richard].

[predicate]
Friends john richard.

When we run [BeliefsOf john ?] we get:

?= [god_exists [important money] [Friends john richard] [Friends john elon_musk]]

The outer brackets mean that it's a tuple.  It has 4 elements, each representing one of John's beliefs:

• god_exists
• [important money]
• [Friends john richard]
• [Friends john elon_musk]

But when we run [BeliefsOf richard ?] we get:

?= [god_exists [important helping_people] [Friends john richard]]

Again, a tuple with each element representing a belief.  But this time, there are only three beliefs.