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A Greek epsilon or lambda standing for a string of no characters.
Also known as: Empty word, Lambda for empty string, Null string symbol
In formal language theory a lowercase epsilon or lambda names the string with no characters in it. Two letters are used for one idea, and the epsilon collides with the epsilon of analysis and with the set-membership sign, which is three meanings for one shape.
Names the empty string: the sequence containing no symbols at all, which is not the same as the empty set.
Contexts: Mathematics
Is written as an epsilon in some traditions and as a lambda in others, with no difference in meaning.
Contexts: Mathematics
A small rounded letter with a horizontal middle bar, or a letter of two strokes meeting at a peak, standing alone in a grammar rule.
One is a string of no characters, the other a set with no members.