I am using plain TeX. I would like to define a macro \cpar that makes

```
\centerline{A\cpar B}

```

expand to

```
\centerline{A}\centerline{B}

```

I have experiemented with things like

```
\def\cpar{\egroup\centerline\bgroup}

```

and various incarnations of \let and \expandafter but couldn't get it to work. Any hints?