  We create mechanical metamaterials whose response to uniaxial compression can
be programmed by lateral confinement, allowing monotonic, non-monotonic and
hysteretic behavior. These functionalities arise from a broken rotational
symmetry which causes highly nonlinear coupling of deformations along the two
primary axes of these metamaterials. We introduce a soft mechanism model which
captures the programmable mechanics, and outline a general design strategy for
confined mechanical metamaterials. Finally, we show how inhomogeneous
confinement can be explored to create multi stability and giant hysteresis.
