RULE 31. YARD WORK. Except as provided in Rule 32, the following shall be considered yard work at terminals were the yardman's schedule is in effect, and shall be handled by yardmen and paid for at not less than yard rates.

(a) The switching or transfer of all freight and passenger equipment operating exclusively within the yard and/or switching limits.

(b) The assembling and breaking-up of all trains or transfers within the switching limits.