clpz:monotonic.

tree(tree(A,Prs))       --> number(X), "x", number(Y), ": ", sequence(number," ",Prs), { #A #= #X * #Y }.
input(Trees)            :- phrase_from_file((...,sequence(tree,"\n",Trees)),"i/12.in").
solvable(tree(A,Prs),T) :- sum(Prs,NPrs), clpz_t(#NPrs*9 #=< #A,T).
solve(P1,":D")          :- input(Trees), tfilter(solvable,Trees,STrees), length(STrees,P1).
test                    :- make_test(day(12),solve,492,":D").

I didn't initially like this problem, but in hindsight, it's pretty fun :D! Happy AoC, and here's to many more!

~/aoc25pl/12