The equations in Activity 1.3.1 should be typeset using <md>, <mrow>, and alignment characters as described here, instead of the <sidebyside>. The current typesetting leads to unequal spacing (because the matrices are slightly different width), which is especially notable in PDF versions.

The equations in Activity 1.3.1 should be typeset using
<md>,<mrow>, and alignment characters as described here, instead of the<sidebyside>. The current typesetting leads to unequal spacing (because the matrices are slightly different width), which is especially notable in PDF versions.