nductively defining function to the type family <code>Xs</code> on W
from the inductive type <code>W = typ</code>;
an implicit <code>mapper</code> is used, which also allows calculation of the type <code>RecType</code>.</p><div class="fullcomment"><div class="comment cmt"><p>returns the term <code>ind_W, X</code> for inductively defining function to the type family <code>Xs</code> on W
from the inductive type <code>W = typ</code>;
an implicit <code>mapper</code> is used, which also allows calculation of the