/* Inspired by code from Python */
Queens(N):=block([K,C,P,V,L:[]],
    C: makelist(K,K,1,N),
    P: permutations(C),
    for V in P do (
        if is(N=length(unique(makelist(V[K]+K, K, C)))) then (
            if is(N=length(unique(makelist(V[K]-K, K, C)))) then (
                L: endcons(V, L)
            )
        )
    ), L
)$

Queens(8);length(%);