Lowercase letters were therefore not interleaved with uppercase. Cyrillic uppercase and lowercase letter forms are not as differentiated as in Latin typography. Most writing systems do not differentiate between uppercase and lowercase letters. There is no differentiation between uppercase and lowercase glyphs. I are separate letters, each with its own uppercase and lowercase forms. I are separate letters, each with its own uppercase and lowercase form. Dictionaries may use lowercase, uppercase, or both. The letter occupies the Unicode slots U+03C4 (lowercase) and U+03A4 (uppercase). Another method consists of simple variations on the existing alphabet; uppercase, lowercase, upside down, etc. Initially, it was a titling font with only uppercase letters. The file's name is generally written in uppercase letters. Gene symbols generally are italicised, with all letters in uppercase (e.g., "NLGN1", for neuroligin1). The uppercase I has two kinds of shapes, with serifs () and without serifs (). The descenders were borrowed from a Byzantine uncial shape of uppercase Delta. He didn't know the difference between lower and uppercase letters.