How to use formulas and expressions in an RHDM rule?

Issue

There are two data objects: DO1 (has fields A, B, C, and D) and DO2 (has fields E, F, G, and H). We want to achieve this in a Guided decision table that has a new column under 'conditions' which has the difference between DO1.A and DO2.E, and have a new column under 'Actions' which takes the difference calculated above (i.e. 3) and compares it against DO1.B (integer). If the result is in a negative, assign value 'NEGATIVE' to the new column and if positive, assign value 'POSITIVE' to the new column.