10 # ExpressionDepth(expression_IsFunction) <--
[
  Local(result);
  result:=0;
  ForEach(item,Tail(Listify(expression)))
  [
    Local(newresult);
    newresult:=ExpressionDepth(item);
    result:=Max(result,newresult);
  ];
  result+1;
];
20 # ExpressionDepth(_expression) <-- 1;
UnFence("ExpressionDepth",1);

