let l'' := congrFun l x₀
case a.a.h
R : Type
inst✝² : Ring R
inst✝¹ : DecidableEq R
X : Type
inst✝ : DecidableEq X
a b : R
x : R[X]
s : FormalSum R X
x₀ : X
l : scmul a s ++ scmul b s ≈ scmul (a + b) s := act_sum a b s
⊢ coords (scmul a s ++ scmul b s) x₀ = coords (scmul (a + b) s) x₀
case a.a.h
R : Type
inst✝² : Ring R
inst✝¹ : DecidableEq R
X : Type
inst✝ : DecidableEq X
a b : R
x : R[X]
s : FormalSum R X
x₀ : X
l : scmul a s ++ scmul b s ≈ scmul (a + b) s := act_sum a b s
l'' : coords (scmul a s ++ scmul b s) x₀ = coords (scmul (a + b) s) x₀ := congrFun l x₀
⊢ coords (scmul a s ++ scmul b s) x₀ = coords (scmul (a + b) s) x₀