Sum (1)(2,3)(4,5,6)

function sum(){
    let arr = [].slice.call(arguments);
    let fn = function(){
    	let arr2 = [].slice.call(arguments);
        return sum.apply(null,arr.concat(arr2));
    }
    
    fn.toString = function(){
    	return arr.reduce((v,n) = > v+n);
    }
    
    return fn;
}
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sum(1) (2.3) (4.5.6) // f 21
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