Learn Prolog Now, Exercises 2.3 Crossword

crossword.prolog

% 2.3
word(astante,  a,s,t,a,n,t,e).
word(astoria,  a,s,t,o,r,i,a).
word(baratto,  b,a,r,a,t,t,o).
word(cobalto,  c,o,b,a,l,t,o).
word(pistola,  p,i,s,t,o,l,a).
word(statale,  s,t,a,t,a,l,e).

crossword(V1, V2, V3, H1, H2, H3) :-
	word(V1, _,V1H1,_,V1H2,_,V1H3,_),
	word(V2, _,V2H1,_,V2H2,_,V2H3,_),
	word(V3, _,V3H1,_,V3H2,_,V3H3,_),
	word(H1, _,V1H1,_,V2H1,_,V3H1,_),
	word(H2, _,V1H2,_,V2H2,_,V3H2,_),
	word(H3, _,V1H3,_,V2H3,_,V3H3,_),
	V1 \= V2,
	V2 \= V3,
	V3 \= H1,
	H1 \= H2,
	H2 \= H3.

output.txt

?- crossword(V1,V2,V3,H1,H2,H3).
V1 = astante,
V2 = baratto,
V3 = statale,
H1 = astante,
H2 = baratto,
H3 = statale 

Better solution, which doesn't use repetitions: https://gist.github.com/ITPol/f8f5418d4f95015b3586#file-crossword-prolog

Can you explain to me what the combined variables do? Like word(V1, ,V1H1,,V1H2,,V1H3,)?

Can you explain to me what the combined variables do? Like word(V1, ,V1H1,,V1H2,,V1H3,)?

Nothing, they are just individual variables named that way for an easier overview.