Question: How do I assume Maple expression to be a constant?

Hello, in a differential equation (in Maple 10) a variable should be replaced by a constant K so that all differentiations of this variable should evaluate to zero. This is my code: constants:= constants, K: myDG1:= u(t) + diff(u(t),t)^2 + v(t)=0: subs(u(t)=K,myDG1); K+(diff(K, t))^2+v(t) = 0 Although I have already assigned K to be constant, Maple doesn't replace d/dt K by 0. Any help would be appreciated.
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