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30267 Coercion via restriction of chart functions gh-mjungmath "At this stage, scalar fields (and tensor fields) support coercions via restrictions:
{{{
sage: M = Manifold(2, 'M')
sage: c. = M.chart()
sage: D = M.open_subset('D')
sage: A = M.scalar_field_algebra(); A_D = D.scalar_field_algebra()
sage: A_D.has_coerce_map_from(A)
True
}}}
But the chart function ring does not support that coercion, even for derived charts:
{{{
sage: c_D = c.restrict(D, x^2+y^2<1)
sage: R = c.function_ring(); R_D = c_D.function_ring()
sage: R_D.has_coerce_map_from(R)
False
}}}
Consequently, this should be treated the same way as scalar fields since chart functions are the very foundation of scalar fields.
I suggest we add that coercion in case one chart (here `c_D`) is the restriction of the other (here `c`)." defect closed major sage-9.2 manifolds fixed egourgoulhon tscrim Michael Jung Travis Scrimshaw, Eric Gourgoulhon N/A d494bbd912c42ca2386664c597b15de117dd52a9 d494bbd912c42ca2386664c597b15de117dd52a9