Diagonal bialgebra action
= Diagonal bialgebra action
{title2=$h(u\otimes v)=\sum h_{(1)}u\otimes h_{(2)}v$}
The tensor of left <modules> over a <bialgebra> has action $h(u\otimes v)=\sum(h_{(1)}u)\otimes(h_{(2)}v)$. The unit module $k$ has action through the <counit>.