On this website in equation (20) they use
$$ d \, S = a \, d \, u \land d \, v $$
I have learned that $\land$ is the truth-functional operator of logical conjunction and that such logical operators are used between expressions evaluating either true or false.
In the equation/expression(?) above, can the two operands(?) $d \, S = a \, d \, u$ and $d \, v$ separately evaluate to a truth value? Otherwise, I haven't understood how to use $\land$ properly.
The wedge product as used in e.g. $\mathrm du \wedge \mathrm dv$ is completely separate from logical conjunction $\alpha\land\beta$.
There are even two TeX commands:
\wedgeand\land, where the latter is to be used for conjunction ("logical and"), to keep the two separated in writing your documents.