Assuming a function is constant in computing later expressions

[Mauricio Calvao]

I have declared a function Omega of a single variable t through:

Omega = function('Omega')(t)

Afterwards, I have calculated a quantity whose generic result is given in terms of the derivative of Omega (let us call it dOmega), for instance:

quanti = Omega(t)*cos(t) + dOmega(t)

Since I know the particular form for this quantity in the case Omega is constant, how can I make Sage assume, in this generic result, that Omega is constant, so that I can really verify the validity of the generic expression in this particular case? Of course we have to recover then:

quanti = Omega(t)*cos(t)

[Eric Gourgoulhon]

What about something like:

sage: t = var('t')
sage: Omega = function('Omega')
sage: quanti = Omega(t)*cos(t) + diff(Omega(t), t)
sage: quanti
Omega(t)*cos(t) + diff(Omega(t), t)
sage: Omega0 = var('Omega0')
sage: Omega_const(t) = Omega0
sage: quanti.substitute_function(Omega, Omega_const)
Omega0*cos(t)

Eric.