the flavor of the days when I was writing code in MMSForth , push the numbers on the stack and then call the operators. Oh, JOY ! (I'll stop now.) > solver = [twiner perms [op1, op2, op3] | > perms@[a,b,c,d] ∈ permute [1..4], > op1 ∈ amb, op2 ∈ amb,