Several other phenomena serve to distinguish regional U.S. accents. Boston, Pittsburgh, Upper Midwestern, and Western U.S. accents have fully completed a merger of the vowel with the vowel ( and , respectively): a "cot–caught" merger, which is rapidly spreading throughout the whole country. However, the South, Inland North, and a Northeastern coastal corridor passing through Rhode Island, New York City, Philadelphia, and Baltimore typically preserve an older "cot–caught" distinction. For that Northeastern corridor, the realization of the vowel is particularly marked, as depicted in humorous spellings, like in "tawk" and "cawfee" ("talk" and "coffee"), which intend to represent it being tense and diphthongal: . A split of into two separate phonemes, using different "a" pronunciations for example in "gap" versus "gas" , further defines New York City as well as Philadelphia–Baltimore accents.