%based on the following code
%TeX by Topic unknown number of arguments p105
%White(K1a,Q2b,3c,P4d)%

defendpiece{xxx}% a sentinel that ends the lists of inputs
defdosomethingwithsplitofpiece#1{*#1}

defsep{,}

defxSplit#1,{deftemp{#1}% replace , by sep
ifxtempendpiece% no more to process
else%
   dosomethingwithsplitofpiece{#1}%
   expandafterxSplit%
fi%
}%

defSplit(#1){#1 transforms into xSplit#1,xxx,% >-- how this comma as a variable
                                                % that can be changed if necessary??
}%

Split(4,5,6,7,9,10,11)
 % Split(4,5,6;7,9,10;11){1}

bye