Given a set $X$ and a relation $R$ over $X$, we say that $R$ is reflexive if \begin{equation} xRx\ \forall\ x\in X. \end{equation} What does 'identitive' mean? Is it the same as antisymmetry?
Seen in Struwe's book Variational Methods: Applications to nonlinear PDE's and Hamiltonian systems, 4th ed., p.52:
Your guess is correct: Google Books gave me a look at p. $52$ of Struwe, Variational Methods, and it’s very clear that he’s using the term identitive to mean antisymmetric.