Disjunctive ordering

Disjunctive ordering is a type of rule interaction, introduced by Chomsky &amp; Halle (1968). Two rules A and B are ordered disjunctively if rule B may not be applied to the output of rule A, even if the output of rule A satisfies the structural description of rule B. See also parenthesis notation.

Example
rule (a) and (b) are two rules among the stress rules of English:

a	V -&gt;	   V    / ____C_0VC0 [+stress] b	V -&gt;	   V    / ____C0 [+stress]

Rule (a) is applied in ellípsis ; Rule (b) could then in principle also apply yielding the incorrect ellí­psís (with two main stresses). Therefore, rule (a) and (b) are ordered disjunctively to prevent rule (b) from applying after rule (a) has applied.

Link
Utrecht Lexicon of Linguistics