A.6.3.RT.OE:5.2 - Preserve a shared prerequisite in a grouped instruction

A working convention uses “then” for ordered performance and “or” for choosing one continuation. The intended content is: perform A, then choose B or C.

Prepare:

A then (B or C).

The parentheses make B or C the second contribution. The allowed completed sequences are A followed by B and A followed by C.

Compare the alternative grouping:

(A then B) or C.

Under the same convention, it permits A followed by B or C on its own. The letters and operation words are unchanged, but the expression no longer requires A before C. A reader following C without A exposes the difference.

Retain the first grouping when A is a common prerequisite. For example, if A establishes the coordinate reference used by either subsequent construction, the second grouping permits a construction without that reference. The repair changes grouping; it requires no new vocabulary or new domain Method.

If the original work instead permits C independently, the second expression is appropriate. The source work determines that choice.