let counter = 0;
let output = "";
const print = (txt) => output += txt;
const printPreceded  = (precede, txt) => output += (precede ? ", " : "") + txt;
const are_pair = (a, b) => a %2 === 0 && b%2 ===0;
const process = (precede, a,b) =>  are_pair(a,b) ? printPreceded(precede, a+b)
                                 : a === b ? printPreceded(precede, a)
                                 : printPreceded(precede, counter);
const run= (name1, arr1, name2, arr2) => {
    print(`\ncomparing ${name1} and ${name2}\n`);
    let flag = 0;
    for(i of arr1)
    for(j of arr2){ ++counter; process(flag++, i, j); }
}
const a = [7,6,5,4]; const b = [9, 7, 5 , 3 ] ; const c = [4,6,8,2];
counter = 0; run("apple", a, "samsung", b); run("apple", a, "huawei", c); run("huawei", c, "samsung", b);
console.log(output);