## Coordinate

Declare a symbol to be a coordinate label.

Declare a symbol to be a coordinate label (useful in combination
with `Depends`

). This is required if you want to write a
derivative with respect to a coordinate: if you write\partial{#}::PartialDerivative.
ex:= A(x,y) + \partial{B(x,y)}_{x};

\(\displaystyle{}A((x, y))+\partial(B((x, y)))\,_{x}\)

will by default be seen as incorrect because the $x$ in the second
term will be considered an index label, not a coordinate. The input

{ x, y }::Coordinate.
ex:=A(x,y) + \partial{B(x,y)}_{x};

\(\displaystyle{}A((x, y))+\partial(B((x, y)))\,_{x}\)

is allowed and interpreted in the right way.