<P> The nabla is a triangular symbol like an inverted Greek delta: ∇ (\ displaystyle \ nabla) or ∇ . The name comes, by reason of the symbol's shape, from the Hellenistic Greek word νάβλα for a Phoenician harp, and was suggested by the encyclopedist William Robertson Smith to Peter Guthrie Tait in correspondence . </P> <P> The nabla symbol is available in standard HTML as &nabla; and in LaTeX as \ nabla . In Unicode, it is the character at code point U + 2207, or 8711 in decimal notation . </P>

What is the upside down triangle in calculus