Optimal error bounds for the MITC4 plate bending element

One of the most popular finite element method for Reissner-Mindlin plates is the so-called MITC4 method. Unfortunately, until recently, the best error estimate available in the literature for this element needs a non-optimal and generally unrealistic regularity for the solution. Here we derive optimal error estimates for this well-known low-order finite element method, which are valid for a general family of meshes. A similar result has recently been obtained elsewhere, with the same mesh restrictions. The exposition presented here is totally different