\ulcorner \urcornerThe symbols \ulcorner and \urcorner are used in mathematical logic to denote the corner brackets, often used to enclose expressions or formulas. They are typically used to indicate the Gödel number or code of a formula.
Gödel number of the formula A
\ulcorner A \urcornerEncoding of the formula \phi(x)
\ulcorner \phi(x) \urcornerGödel number of a quantified formula
\ulcorner \exists x \forall y (x = y) \urcorner