assigning a value to anonymous variable in prolog
<p>I want to mary two person. I defined X and Y in top of grammar.
My grammar is: <code>evlendir(X,Y):-</code> 
I write following code but I can not compare D and B with 1998. 
D is refer to birthdate of <code>male(X,_,_)</code> and B is refer to birthdate of <code>female(X,_,_)</code> 
and also my database is like male(name,birthdate,deathdate) : </p>

<p><code>male(orhan,1978,_).
male(tolga,1982,_).
</code>
<code>female(secil,1975,_).
female(derya,1982,_).
</code>
PLEASE HELP ME.
<a href="https://i.stack.imgur.com/cVHaS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cVHaS.png" alt="enter image description here"></a></p>