Q:

Create Prolog Vocabulary

i am quite new to prolog, and i have some basic questions...
I dont know if "vocabulary" is the right world in english, but i need to create one to describe an eletronic circuit.
My problem is, how do i create these functions and how i use the "=" statement since prolog doesnt seems do acept it.
Im using SWI Prolog.
(tried my best to translate to english)Thats what i have to put in prolog:
Decide the vocabulary (Predicates, functions, constants):
Ports are represented by constants (X1, X2, ...) – 
Gate(X1)
Type(X1) = Xor – types: AND, OR, XOR or NOT
Circuits(C1)
Terminals(x) – returns inputs and outputs of x
In(1, X1) – function that returns first input of X1
Out – function that returns output 
Arity(c, i, j) – function, circuit c has i inputs and j outputs
Connected(Out(1, X1), In(1, X2)) - wich ports are conected
Signal(t) – signal value for terminal t.
Thtas what i tried until now. I dont think my approach to the "=" is right...
gate(x1).
gate(x2).
gate(a1).
gate(a2).
gate(o1).
type(x1, xor).
type(x2, xor).
type(a1, and).
type(a2, and).
type(o1, or).
circuit(c1).

Should i use an predicate named Equal(X, Y) ?, like "equal (type(x1), xor).
How should i implement these?
Gate(X1) , Type(X1) = XOR
Gate(X2) , Type(X2) = XOR
Gate(A1) , Type(A1) = AND
Gate(A2) , Type(A2) = AND
Gate(O1) , Type(O1) = OR 

I dont know how to continue from here. All my approachs trying to implement the functions seems to be wrong (cant consult).

A:

You should read this document to get some inspiration :)
For instance, basic functions (i.e. gates) can be described like
and(0, 0, 0).
and(0, 1, 0).
and(1, 0, 0).
and(1, 1, 1).

xor(0, 0, 0).
...

and then combined to get more complex building blocks
fulladder(A, B, Carryin, Sum, Carryout):-
 xor(A, B, X),
 and(A, B, Y),
 and(X, Carryin, Z),
 xor(Carryin, X, Sum),
 or(Y, Z, Carryout).

that compute the logic function:
?- fulladder(X, Y, Z, 0, 1).
X = 0, Y = 1, Z = 1 ? ;
X = 1, Y = 0, Z = 1 ? ;
X = 1, Y = 1, Z = 0 ? ;
no

