Model-independent implications of the isostructure of currents for $\ensuremath{\gamma}\ensuremath{-}$, $e\ensuremath{-}$, $\ensuremath{\nu}\ensuremath{-}$, and $\overline{\ensuremath{\nu}}$-induced production reactions are noted. Reactions on hydrogen and deuterium only are considered; separate neutron information is not used. Numerous tests are given for the absence of $I=2$ (or specific higher $I$ values), for the electromagnetic current, and for the weak $\ensuremath{\Delta}S=0$ current (independent of class). Similar results are derived for the $|\ensuremath{\Delta}I|=\frac{1}{2}$ rule for $|\ensuremath{\Delta}S|=1$ currents, where $\overline{\ensuremath{\nu}}\ensuremath{-}d$ reactions are most favorable. A consequence for ${K}_{14}$ decays is mentioned. The expansion of cross sections in terms of the azimuthal angle between the lepton and a hadron plane yields equalities implied by the absence of second-class currents (independent of isospin content) in $T$-conserving situations. Here the $\ensuremath{\nu}$ and $\overline{\ensuremath{\nu}}$ disintegrations of the deuteron are of special interest.
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