tangent vectors

Define rules for the tangent vectors.

check if they work

Next, we will calculate below.

Apply the separate operator to phi2eta=, and evaluate it on the surface to get phi2u=.

Using phi2u above, we write phi2bu= as follows. First, the summation range of phi2bu is separated into type-a and dim. Then,   are substituted by their expressions.

We may symmetrize the coefficients of phi2bu.

Further simplification is possible. Here the phi2bu is essentially the same as above although the warning messages appear.