Curl of scalar function in 2D should be vector

[yguclu]

When taking the curl of a scalar function in 2D, this should be interpreted as the vector Curl operator, whose result is a vector with two components.

SymPDE thinks instead that the result is scalar, as can be checked with this code:

from sympde.topology import Square, ScalarFunctionSpace, element_of
from sympde.calculus import curl

domain  = Square('Omega')
V = ScalarFunctionSpace('V', domain)
u = element_of(V, name='u')
expr = curl(u)

print(expr.is_scalar)

This incorrectly prints True to terminal, instead of False.

The correct result is obtained by replacing curl with rot.