Genetic tree in prologue, where am I wrong?

Question

Prolog

Given a genetic tree, it is
necessary to find out who is who's brother-in-law.
Brother-in-law is the wife's brother.

did like this

predicates
  parent (symbol, symbol)
  man (symbol)
  woman (symbol)
  shurin (symbol, symbol)
  suprugi (symbol, symbol)

clauses
   parent (barbara, liza).
   parent (valera, liza).
   parent (barbara, nikolay).
   parent (valera, nikolay).
   parent (anna, katya).
   parent (anna, petr).
   parent (srgey, katya).
   parent (srgey, petr).
   parent (tatiana, natali).
   parent (tatiana, mihail).
   parent (dmitry, natali).
   parent (dmitry, mihail).
   parent (liza, alex).
   parent (petr, alex).   
   parent (nikolay, raisa).
   parent (natali, raisa).
   parent (katya, alexandr).
   parent (mihail, alexandr).
   parent (katya, juli).
   parent (mihail, juli).
   parent (alex, kostya).
   parent (juli, kostya).
   parent (raisa, lyuda).
   parent (alexandr, lyuda).
   suprugi (barbara, valera).
   suprugi (anna, sergey).
   suprugi (tatiana, dmitry).
   suprugi (liza, petr).
   suprugi (nataly, nikolay).
   suprugi (katya, mihail).
   suprugi (raisa, alexandr).
   suprugi (juli, alex).
   suprugi (lyuda, kostya).
   man (valera).
   man (sergey).
   man (dmitry).
   man (nikolay).
   man (petr).
   man (mihail).
   man (alex).
   man (alexandr).
   man (lyda).
   woman (barbara).
   woman (anna).
   woman (tatiana).
   woman (liza).
   woman (katya).
   woman (nataly).
   woman (raisa).
   woman (juli).
   woman (lyuda).
   

shurin (y,x) :-
   parent (z,k),
   parent (z,y),
   suprugi (k,x),
   man (y).
   

goal
   shurin (y, x),
   write (y, "shurin", x).

but as a result of the answer I get just "no"
where did I go wrong?
thanks in advance

Answer 1

The main code of the rules.
1. Variables must be capitalized, otherwise they are considered values.
2. In the original data you have a lot of typos, as a result sergey is sometimes srgey, natali is nataly, and kostya is not a man at all. Etc.
3. You get duplicates because both parents are checked. If you add a check for only one parent (for example, only mother or father), then the duplicates will go away.
Something like this.