Major difficulties associated with attempts to describe the $\mathrm{YN}$ (hyperon-nucleon) interaction in all $\Lambda$-hypernuclear systems having $A\le 4$ by simple, effective $\Lambda p$ and $\Lambda n$ potentials are examined. The explicit $A$ dependence of the $\mathrm{YN}$ interaction associated with each system is explored, and the necessity of using exact four-body theory (in the $A=4\mathrm{}$ system) to calculate small charge-symmetry-breaking effects in terms of $\Lambda N$ potentials fitted to free $\Lambda$ scattering data is discussed.

NUCLEAR STRUCTURE $\Lambda N$ interactions; ${}_{\Lambda }{}^3{}_{}{}^{}\mathrm{H}$, ${}_{\Lambda }{}^4{}_{}{}^{}\mathrm{H}$, ${}_{\Lambda }{}^4{}_{}{}^{}\mathrm{He}$; $\Lambda -\Sigma$ coupling.

• Received 28 April 1980

DOI:https://doi.org/10.1103/PhysRevC.23.573