  We show that the lower-semicontinuous envelope of a non-convex double
integral may not admit a representation as a double integral. By taking an
integrand with value $+\infty$ except at three points (say $-1$, $0$ and $1$)
we give a simple proof and an explicit formula for the relaxation that
hopefully may shed some light on this type of problems. This is a simplified
version of examples by Mora-Corral and Tellini, and Kreisbeck and Zappale, who
characterize the lower-semicontinuous envelope via Young measures.
