+// for integrals:
+// cell(0) is stuff before the 'd'
+// cell(1) is the stuff after the 'd'
+// cell(2) is the lower bound
+// cell(3) is the upper bound
+// for sums:
+// cell(0) is the main body
+// cell(1) is the index (e.g., i), if the lower bound is "i = ..."
+// or the whole lower bound if not
+// cell(2) is what follows the "=" in the first case
+// cell(3) is the upper bound