`solve vSolve(u, v) = a(u, v) + l(v)`

solves `a(u, v) + l(v) = 0`

while `varf vPb(u, v) = a(u, v) + l(v)`

solves `a(u, v) = l(v)`

, so it is expected that you need to shift the sign in front of the linear form.

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