:Obligatory contour principle:

Usually abbreviated to OCP. A phonological principle which was originally formulated to disallow adjacent identical tones in the lexical representation of a morpheme. See Leben (1973). The idea has since been extended beyond the phonology of tone to phenomena involving other features.

For more detail see van Oostendorp (2005).

Leben, W. (1973) Suprasegmental Phonology. PhD dissertation, MIT. Distributed by Indiana University Linguistics Club.